Dissertations / Theses on the topic 'Adsorption, Density Functional Theory'
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Mulakaluri, Narasimham. "Density functional theory investigation of water adsorption on the Fe3O4(001) surface." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-121376.
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Sayin, Ceren Sibel. "Density Functional Theory Investigation Of Tio2 Anatase Nanosheets." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12611075/index.pdf.
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In this thesis, the electronic properties of nanosheets derived from TiO2 anatase structure which acts as a photocatalyst, are investigated using the density functional theory. We examine bulk constrained properties of the nanosheets derived from the (001) surface and obtain their optimized geometries. We investigate properties of lepidocrocite-type TiO2 nanosheets and nanotubes of different sizes formed by rolling the lepidocrocite nanosheets. We show that the stability and the band gaps of the considered nanotubes increase with increasing diameter. We also study adsorption of
Aun clusters with (n=1,2,3,4) on the clean and oxygen depleted lepidocrocite surface. Through systematic investigation of various cases we conclude that Au preferres O
vacancy sites rather than clean surface in accordance with previous metal adsorption studies on TiO2 surfaces. For the clean surface, we observe that Au clusters with an odd number of atoms are weakly bonded and metallizes the system while even number of Au atoms results in small band gap semiconductors with relatively higher binding energies.
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Guhl, Hannes. "Density functional theory study of oxygen and water adsorption on SrTiO 3 (001)." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2011. http://dx.doi.org/10.18452/16276.
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Strontiumtitanat ist ein häufig untersuchtes Oxidmaterial, mit einem breiten Anwen- dungsgebiet z.B. in der Photokatalyse oder auch als Substratmaterial beim Wachstum ande- rer Oxidschichten. Dabei spielen chemische Prozesse an der Oberfläche eine herausragende Rolle, deren Kenntnis für eine tieferes Verständnis der genannten Anwendungen unentbehrlich ist. Darüberhinaus gibt es deutliche Hinweise darauf, dass diese Oberflächenprozesse sehr stark, u.a. von Wasserstoff und Wasser beeinflußt werden. Sowohl wegen der Relevanz als auch wegen der technischen Machbarkeit, stellt eine Untersuchung des Adsorptionsverhaltens von Sauerstoff und Wasserstoff mit Hilfe der Dichtefunktionaltheorie einen natürlichen Ausgangspunkt dar, um genaue Einblicke in die Prozesse auf der Oberfläche auf atomare Ebene zu gewinnen. Bei der Adsorption des Sauerstoffs und des Wassers ist gleichermaßen auffällig, dass die Bindungsenergien sehr stark durch langreichweitige Verzerrungen im Substratgitter beeinflußt werden, welche damit eine effektive repulsive Wechselwirkung der adsorbierten Spezies bewirken. Adsorbierte Sauerstoffatome bilden mit jeweils einem Sauerstoffatom des Subtrats ein „Quasi-Peroxid-anion“, wodurch das adsorbierte Sauerstoffatom einen Gitterplatz einnimmt, der nicht einem Sauerstoffplatz des Perovskitgitters entspricht. Im Gegensatz dazu wurden bei allen untersuchten atomaren Konfigurationen, die Wasser und Hydroxylgruppen enthielten, beobachtet, dass sich hier die adsorbierten Sauerstoffatome an den Plätzen des forgesetzten Perovskitgitters befinden. Bemerkenswert ist die spontane Dissoziation und Bildung eines Hydroxylpaares auf der Strontiumoxidterminierung während des Adsorption des Wassermoleküls. Auf der Titandioxidterminierung hingegen werden abhängig von der Bedeckung Wassermoleküle und Hydroxylgruppen beobachtet. Die Energetik, die diesem Verhalten zugrunde liegt, zeigt sehr gute Übereinstimmung mit den experimen- tellen Beobachtungen von Iwahori und Kollegen.Strontium titanate is an extensively studied material with a wide range of application, for instance in photo-catalysis and most importantly, it is used as a substrate in growth of functional oxides. The surface chemistry is crucial and hence understanding the surface structure on atomic scale is essential for gaining insight into the fundamental processes in the aforementioned applications. Moreover, there exist a lot of evidence that this surface chemistry might be controlled to considerably by extrinsic species, such as residual hydrogen and water. Investigating the properties of water and oxygen on the strontium titanate surface is certainly a natural starting point for a theoretical study based on density functional theory, because these species are practically present on the surface on a wide range of experimental conditions and they are computationally feasible. For the oxygen and water adsorption the binding energy is controlled by long-range surface relaxations leading to an effective repulsion of the adsorbed specimen. The isolated oxygen ad-atom forms a covalently bonded “quasi-peroxide anion” in combination with a lattice oxygen atom. Contrariwise, in all investigated configurations containing water molecules and hydroxyl groups, the respective oxygen atoms assumed positions close to the oxygen sites of the continued perovskite lattice of the substrate. Most remarkably, on the strontium oxide termination, the water molecules adsorbs and dissociates effortlessly leading to the formation of a pair of hydroxyl groups. For the titanium dioxide termination, a coverage dependent adsorption mode is observed. Densely packings stabilize water molecules, whereas at lower coverage and finite temperatures the formation of hydroxyl groups is found. The energetics responsible for this behavior is consistent with recent experiments by Iwahori and coworkers.
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Han, Jeong Woo. "Density functional theory studies for separation of enantiomers of a chiral species by enantiospecific adsorption on solid surfaces." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34848.
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The distinct response of biological systems to the two enantiomers of a chiral chemical has led to a large market for enantiopure pharmaceuticals and raised fundamental issues about the origin of biological homochirality. It is therefore important to understand the interactions of chiral molecules with chiral environments. Chiral environments associated with solid surfaces could potentially play a useful role in chirally specific chemical processing. There are a variety of routes for creating chiral solid surfaces. Surfaces of materials whose bulk crystal structure is enantiomorphic can be used as one type of chiral solid surfaces. Metal surfaces that are intrinsically chiral due to the presence of kinked surface steps provide another route for creating chiral solid surfaces. Alternatively, we can impart chirality onto surfaces by attaching irreversibly adsorbing chiral organic species on otherwise achiral surfaces. Understanding and ultimately controlling enantiospecific interactions of molecules on this kind of surfaces requires detailed insight into the adsorption geometries and energies of these complex interfaces. To tackle these issues, we performed density functional theory (DFT) calculations that have proved to be a useful tool for quantitative prediction of these effects. Besides our main topic above, we theoretically examine the effects of K atoms as a promoter coadsorbed with small molecules on Mo2C surfaces, a promising catalyst for a range of chemicals applications. Our results in this thesis provide fundamental information about these systems and demonstrate that using DFT for this purpose can be a useful means of identifying the phenomena that control chiral surface chemistry.
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Scaife, S. J. "The characterisation of porous carbons using computer modelling and experimental techniques." Thesis, Bangor University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310862.
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KIM, BO GYEONG. "Mercury-Containing Species and Carbon Dioxide Adsorption Studies on Inorganic Compounds Using Density Functional Theory." Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/193659.
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The goal of this research is to obtain the adsorption mechanisms of toxic mercury-containing species (Hg, HgCl and HgCl2) and carbon dioxide (CO2) on inorganic solid surfaces using theoretically predicted results because experiments have been unable to unravel the involved issues. The understanding of the adsorption mechanisms of the mercury species and carbon dioxide from flue gases is important when considering mercury capture from coal-fired power plants, artisanal gold mining, and cement manufacturing industries. The current research attempts to explain each adsorption mechanism for mercury species, and those for carbon dioxide adsorption, on the surfaces through optimized geometries, energies and thermodynamic data.To investigate this research, density functional theory, which is one of useful tools for analyzing reactions on solid surfaces, was used to determine first principles-based theoretical adsorption models. Mainly, results from computational work indicate that mercury-containing species and carbon dioxide adsorption on calcium oxide surfaces and elemental mercury adsorption on a gehlenite surface are exothermic reactions. Calcium oxide is a promising adsorbent for oxidized mercury (HgCl and HgCl2), but not for elemental Hg. Interestingly, the elemental mercury, which is the major form (> 90%) in the flue gases of the coal-combustion power plants, is chemisorbed on a gehlenite surface, which is partially composed of calcium oxide and comes from a mineral transition at high temperature. Strong adsorption on this inorganic sorbent is enhanced at high temperatures even though this adsorption process is exothermic. In addition, CaO surfaces are effective at capturing CO2, generating calcium carbonate compounds at flue gas temperatures, and water vapor enhances its adsorbability due to a larger CO2 adsorption energy. The current research shows that inorganic sorbents are not only effective in removing the elemental and oxidized forms of mercury but also in mineralizing CO2 at high temperatures into a solid form. The mercury species and carbon dioxide adsorption mechanisms investigated in this research may be utilized in the application of more efficient mercury and carbon dioxide control technologies. Future work will examine the reaction transition state and predict the kinetic data of the carbonation reactions, and, additionally, may prove the hypothesis that H2O molecules play a role as catalysts, increasing reaction rates.
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Patra, Abhirup. "Surface properties, adsorption, and phase transitions with a dispersion-corrected density functional." Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/516784.
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PhysicsPh.D.
Understanding the “incomprehensible” world of materials is the biggest challenge to the materials science community. To access the properties of the materials and to utilize them for positive changes in the world are of great interest. Often scientists use approximate theories to get legitimate answers to the problems. Density functional theory (DFT) has emerged as one of the successful and powerful predictive methods in this regard. The accuracy of DFT relies on the approximate form of the exchange-correlation (EXC) functional. The most complicated form of this functional can be as accurate as more complicated and computationally robust method like Quantum Monte Carlo (QMC), Random Phase Approximation (RPA). Two newest meta-GGAs, SCAN and SCAN+rVV10 are among those functionals. Instantaneous charge fluctuation between any two objects gives rise to the van der Waals (vdW) interactions (often termed as dispersion interactions). It is a purely correlation effect of the interacting electrons and thus non-local in nature. Despite its small magnitude it plays a very important role in many systems such as weakly bound rare-gas dimers, molecular crystals, and molecule-surface interaction. The traditional semi-local functionals can not describe the non-local of vdW interactions; only short- and intermediate-range of the vdW are accounted for in these functionals. In this thesis we investigate the effect of the weak vdW interactions in surface properties, rare-gas dimers and how it can be captured seamlessly within the semi-local density functional approximation. We have used summed-up vdW series within the spherical-shell approximation to develop a new vdW correction to the meta-GGA-MS2 functional. This method has been utilized to calculate binding energy and equilibrium binding distance of different homo- and hetero-dimers and we found that this method systematically improves the MGGA-MS2 results with a very good agreement with the experimental data. The binding energy curves are plotted using this MGGA-MS2, MGGA-MS2-vdW and two other popular vdW-corrected functionals PBE-D2, vdW-DF2. From these plots it is clear that our summed-up vdW series captures the long-range part of the binding energy curve via C6, C8, and, C10 coefficients. The clean metallic surface properties such as surface energy, work functions are important and often play a crucial role in many catalytic reactions. The weak dispersion interactions present between the surfaces has significant effect on these properties. We used LDA, PBE, PBSEsol, SCAN and SCAN+rVV10 to compute the clean metallic surface properties. The SCAN+rVV10 seamlessly captures different ranges of the vdW interactions at the surface and predicts very accurate values of surface energy ( ) , and work function (𝞥) and inter-layer relaxations (𝞭%). Our conclusion is adding non-local vdW correction to a good semi-local density functional such as SCAN is necessary in order to predict the weak attractive vdW forces at the metallic surface. The SCAN+rVV10 has also been employed to study the hydrogen evolution reaction (HER) on 1T-MoS2. We have chosen as a descriptor differential Gibbs free energy (𝚫 GH ) to understand the underlying mechanism of this catalytic reaction. Density functional theory calculations agree with the experimental findings. In the case of layered materials like 1T-MoS2, vdW interactions play an important role in hydrogen binding, that SCAN+rVV10 calculation was able to describe precisely. We have also used SCAN and SCAN+rVV10 functionals to understand bonding of CO on (111) metal surfaces, where many approximations to DFT fail to predict correct adsorption site and adsorption energy. In this case SCAN and SCAN+rVV10 do not show systematic improvements compared to LDA or PBE, rather, both SCAN and SCAN+rVV10 overbind CO more compared to PBE but less compared to the LDA. This overbinding of CO is associated with the incorrect charge transfer from metal to molecule and presumably comes from the density-driven self-interaction error of the functionals. In this thesis we assessed different semi-local functionals to investigate molecule surface systems of 𝞹-conjugated molecules (thiophene, pyridine) adsorbed on Cu(111), Cu(110), Cu(100) surfaces. We find the binding mechanism of these molecules on the metallic surface is mediated by short and intermediate range vdW interactions. Calculated values of binding energies and adsorbed geometries imply that this kind of adsorption falls in the weak chemisorption regime. Structural phase transitions due to applied pressure are very important in materials science. However, pressure induced structural phase transition in early lanthanide elements such as Ce are considered as abnormal first order phase transition. The Ce 𝝰-to-𝝲 isostructural phase transition is one of them. The volume collapse and change of magnetic properties associated with this transition are mediated by the localized f-electron. Semi-local density functionals like LDA, GGA delocalize this f-electron due to the inherent self-interaction error (SIE) of these functionals. We have tested the SCAN functional for this particular problem, and, it was found that the spin-orbit coupling calculations with SCAN not only predicts the correct magnetic ordering of the two phases, but also gives a correct minima for the high-pressure 𝝰-Ce phase and a shoulder for the low-pressure 𝝲-Ce phase.
Temple University--Theses
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Muscenti, Thomas Michael. "Density Functional Theory Study of Rutile SiO₂ Stishovite: An Electron Pair Description of Bulk and Surface Properties." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/10179.
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The bulk structure and the nonpolar, stoichiometric (110) surface of stishovite, rutile structure type SiO₂, has been studied using a first principles, density functional method. The geometric and electronic structure, including the density of states, charge density, and electron localization function for both the bulk and the surface have been examined. The electron pair properties of both bulk and surface-layer atoms were found to be similar to molecular analogs. The analogs allowed for the description of surface electronic structure using simple molecular models. The adsorption of hydrogen fluoride was studied on the (110) surface. The geometry optimized and electronic structure have been found for various initial geometries. Relaxed structures of certain initial geometries give dissociated hydrogen fluoride upon geometry optimization.Master of Science
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Edwards, Angela Celeste. "Probing the Hydrogen Bonding Interaction at the Gas-Surface Interface using Dispersion Corrected Density Functional Theory." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/71784.
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he interactions of the chemical warfare agent sulfur mustard with amorphous silica were investigated using electronic structure calculations. In this thesis, the binding energies of sulfur mustard and mimic species used in the laboratory were calculated using density functional theory and fully ab initio calculations. The wB97XD and B97D functionals, which include functions to account for long-range dispersion interactions, were compared to experimental trends. The hydroxylated amorphous silica surface was approximated using a gas-phase silanol molecule and clusters containing a single hydroxyl moiety.
Recent temperature programmed desorption experiments performed in UHV concluded that sulfur mustard and its less toxic mimics undergo molecular adsorption to amorphous silica. Hydrogen bonding can occur between surface silanol groups and either the sulfur or chlorine atom of the adsorbates, and the calculations indicate that the binding energies for the two hydrogen bond acceptors are similar. The adsorption of sulfur mustard and its mimics on silica also exhibits the presence of significant van der Waals interactions between alkyl of the adsorbates and the surface. These interactions, in combination with the formation of a hydrogen bond between a surface silanol group and the Cl or S atoms of the adsorbates, provide remarkably large binding energies.Master of Science
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Widjaja, Hantarto. "Geometrical and orientation investigations on the electronic structures of elements adsorption on graphene via density functional theory." Thesis, Widjaja, Hantarto (2016) Geometrical and orientation investigations on the electronic structures of elements adsorption on graphene via density functional theory. PhD thesis, Murdoch University, 2016. https://researchrepository.murdoch.edu.au/id/eprint/31440/.
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Nano-sized materials have promising contemporary and novel technological applications as they possess favourable properties due to quantum effects. The nano-sized graphene material exhibits remarkable electrical, optical, thermal and mechanical characteristics. Adding impurities or doping constitutes an effective way in fine-tuning properties of graphene for specific applications. This study aims to investigate the geometrical aspects of elements adsorption on graphene to produce more accurate models of the electronic structure of graphene as a result of the doping.
Previous models investigated mainly the adsorption sites (bridge, hollow, top); however, they could not systematically explain certain phenomena, e.g. nonlinearity of band gaps to atomic ratios in oxygen-adsorbed graphene. We hypothesise that this is attributed to the positions and orientation of the adatoms (adsorbed elements) relative to one another, which is, in essence, a geometrical phenomenon.
In the present study, geometrical investigations of elemental adsorption on graphene focused on side (single-, double-sided), site (bridge, hollow, top) and orientation (the position of adatom relative to one another and graphene). The computational simulations were conducted by using the generalized gradient approximation (GGA) functional within the density functional theory (DFT) framework. The VASP (Vienna Ab initio Simulation Package) software was utilised for all simulations.
Trends in the elemental adsorption on graphene in terms of sides/sites/orientations are presented in terms of: binding energy (stability); migration (barrier) energy; adatom height; graphene distortion; Fermi energy; magnetization; charge transfer and energy band gap. The calculated results of 10 elements (Na, Mg, Al, Si, P, S, F, Cl, Br and I) adsorbed on pristine graphene indicate that the geometrical combination of side, site and orientation is vital in determining the most stable configuration of the adsorbed systems. This study reinforces the notion that the involvement of site/orientation of element (or functional group) is essential in future models of adsorption on graphene.
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Oftadeh, M., M. Totonkooban, and N. Farzi. "Study of the Structure Effect on Water Adsorption by a Group of Nano Copper Clusters." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35138.
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According to the previous studies, water adsorption energy on the metal surface like as Cu strongly dependent
to the structure surface and the size. During the study of the mechanism of the interaction of water
and Cu in water gas shift reaction (WGSR) (CO + H2O CO2 + H2), it has been determined Cu is active
site of catalysis. These studies inspired the authors to consider theoretically the effect of the structure
in the process of the water adsorption in order to select the suitable structures of the copper clusters, Cu10,
for H2 releasing in the fuel cells at B3LYP/6-31G level of theory. The results showed the distinct effect of
the structure on the type of adsorption process (physical or chemical) through three structure of Cu10 (I, II,
III structures, Fig. 1). The structures I and II showed physical surface adsorption in reaction with water
and the structure III showed chemical adsorption with H2 releasing. The adsorption energies are 0.38 ,1.15
,-28.27 (kcal/mol) and ΔGads are 11.14, 13.49, -20.12 (kcal/mol), respectively.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35138
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Mann, Rajinder K. "Adsorption and reaction of ketones on the surface of group 10 metal catalysts, a density functional theory study." Thesis, Cardiff University, 2004. http://orca.cf.ac.uk/55561/.
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The hydrogenation of ketones over cinchona modified transition metal surfaces is an important step in many applications in heterogeneous catalysis, such as the production of unsaturated alcohols from a-0 unsaturated ketones. In the gas-phase simple ketones, such as acetone, do not have a significant population of the enol isomer. Even so deuterium exchange studies clearly point to the involvement of the enol form in hydrogenation catalysis over some group 10 metals. Two different aspects of the nature of the intermediates involved in the model enantioselective hydrogenation reaction are investigated in this work. In Chapter 5, a combined semi-empirical and ab initio conformational analysis of cinchonidine reveals four stable structures of the alkaloid, two Open and two Closed forms. The reaction energies for the formation of the diastereomeric complex between protonated cinchonidine conformers and the s-cis and s-trans isomers of ethyl pyruvate and butane-2,3-dione are used to predict the relative concentrations of these intermediates. For both reactants, the complex involving the Open(3)H+ structure with the s-cis conformation of the reactant, favouring the pro (R) lactate and hydroxybutanone are optimised to be the dominant intermediates formed in the hydrogenation reaction, providing theoretical enantiomeric excesses of 33% and 98%, respectively. In Chapters 6 and 7, periodic density functional theory calculations are used to examine the chemisorption of formaldehyde and acetone as model keto groups for the pyruvate on (111) surfaces of Pd and Pt. To test computational methods the adsorption of ethene on Pt(III) is investigated. The CASTEP program is found to overbind the ethene molecule to the surface. The corresponding adsorption energies are overestimated by between 10 and 20% when compared to analogous data generated with the VASP code. The overestimation is caused by the use of ultrasoft pseudopotentials generated at the local density approximation level. Reliable adsorption data for the chemisorption of formaldehyde and acetone is obtained with the VASP program, which uses pseudopotentials based on the projector augmented-wave model. The relative energies suggest that the Pt surface is more reactive than the Pd, and that the adsorption of the enol isomer of acetone is thermodynamically stable compared to the keto form. Small activation barriers for the favourable modes of chemisorption are calculated.
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Koh, Wonsang. "First-principles study of the li adsorption on various carbon hybrid systems." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/44845.
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Recent carbon allotropes such as carbon nanotubes (CNTs), fullerenes (C60s) and graphene have attracted great interests in both science and engineering due to their unique properties such as excellent electrical and mechanical properties as well as its vast surface area, and have led to many commercial applications. Especially, CNTs have been considered to be one of the promising candidates in the Li ion battery system because of its outstanding properties. However, the experimental results in the pristine CNT system have shown just slight improvement than original graphitic carbon material, which has been attributed to the weak adsorption of Li on CNTs. In this study, we investigated two types of CNT-C60 hybrid system consisting of CNTs and C60s to improve Li adsorption capabilities and predict its performance through quantum mechanical (QM) computations. First, we investigated adsorption energy of lithium (Li) on dilute CNT-C60 hybrid and CNT-C60 nanobud system as well as various electronic properties such as band structure, density of states (DOS), molecular orbital and charge distribution. Then, we expanded our interest to the more realistic condensed structure of CNT-C60 hybrid and nanobud system to examine actual electrochemical characteristics. The study of the condensed structure has been expanded to the very unique CNT-C60 nano-network system and examined mechanical strength as well as electronic properties. Finally, Li adsorption on other carbon allotropes system such as graphene-C60 hybrid and graphene-C60 bud system was investigated in order to provide fundamental understanding of electronic interaction between carbon allotrope and effect of Li adsorption.
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Yuk, Simuck Francis. "Enantiospecificity of Chiral Pt Nanostructures Grown on Chiral SrTiO3 Surfaces." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1428947746.
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Samsonov, V. M., V. V. Zubkov, and I. V. Grinev. "Comparative Study of Hydrogen Adsorption in Slit-like Pores of Carbon Adsorbents and on Fullerene Molecules." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35172.
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Adsorption of hydrogen in slit-like pores of carbon adsorbents and on fullerene molecules was
investigated using the classical density functional theory. Hydrogen adsorption in a gap between two
graphene walls was calculated at different temperatures and pressures. The obtained results agree with
the data found using the Dubinin theory of the volume pore filling and with the available molecular
dynamics results. It has been shown that conventional carbon adsorbents corresponding to the slit-like
model and fullerene materials should have approximately equal storage capacities. However, such a
capacity is sufficient for practical storage and use of hydrogen at low temperatures only (at about 20 K),
and at room temperatures some special active sites of adsorption should be used to solve the problem
under consideration.
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LIN, HE. "Ab initio study of organic molecules adsorbed on technologically relevant Surfaces." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2016. http://hdl.handle.net/10281/127444.
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In this thesis we investigated materials of relevance to photovoltaics and organic electronics, and the studied systems involving surfaces with technological applications, such as graphene and TiO2 . We make use of the density functional theory (DFT) to calculate the structural and electronic properties of the system, and the Ab initio molecular dynamics to check the temperature dependent effects. Finally, we simulate the core excited spectroscopic measurements by the transition potential approach and use the Time-Dependent DFT to calculate the optical absorption coefficient.
We first focused on covalent adsorption of aromatic radicals onto graphene.. Our results show that the adsorption of an aromatic radical generates two spin-dependent mid-gap states located around the Fermi energy which induce magnetic moments in graphene. This phenomenon can modify the band of pristine graphene and introduces a gap, but this effect is almost independent of the specific chemical functionalization by the aromatic radical. In this way it is possible to magnetize graphene just using s, p electrons without any d-metal impurities. Next we investigated the adsorption of prototypical dyes (catechol and isonicotinic acid) on the TiO2 anatase (101) and rutile (110) surfaces by DFT, Ab initio molecular dynamics and TDDFT calculations. We found that thermal fluctuation induce changes in the position of the molecular levels around the TiO2 valence band edge. For the anatase (101) surface, these fluctuations enhance significantly the low-energy tail of the absorption spectrum, and the sensitization can be improved by increasing the hybridization between the adsorbed dye and TiO2 states. But sensitization effects are less relevant for the rutile (110) surface. As an extension of this work towards more realistic materials for applications, we studied two more complex species, namely PTCDA and PTCDI adsorbed on the TiO2 rutile (110) surface. These molecules determine a more pronounced sensitization effect with a substantial red-shift of the first peak of the dye/TiO 2 absorption relative to the free dye.
Finally, the unoccupied molecular orbitals of corannulene (C20H10 ) were studied by the transition-potential (TP-DFT) approach, and we collaborated with the experimental group of Dr. Andrea Goldoni at ELETTRA, Trieste, Italy who deposited a monolayer of such molecules on Ag (111), and measured X-ray photoemission spectroscopy (XPS) and Near-edge X-ray absorption fine structure (NEXAFS). From our calculation of the intrinsic dichroism resulting from the corannulene curvature and polarization dependent NEXAFS measurement of the unoccupied molecular orbitals, the molecules were found to be oriented at a small tilt angle of ~ 5 degrees from the surface. The molecular tilting results in different electron screening of the core hole in XPS. The corresponding core level shifts broaden the C 1s photoemission peak and produce a splitting of the NEXAFS LUMO resonance, which is strongly contributed by all the C atoms. Higher energy transitions involve different molecular orbitals (π and σ) depending on the excited C atom.
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Neville, Jonathan D. A. "The adsorption and dissociation of water and HF over the surfaces of aluminium oxide polymorphs, a density functional theory study." Thesis, Cardiff University, 2004. http://orca.cf.ac.uk/55517/.
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Quantum mechanical approaches to selecting the most accurate method of calculation for the bulk structure of alpha-alumina. The aluminium terminated {0001} surface is then fully analysed, followed by the hydroxylated {0001} alpha-alumina surface, formed by the Dissociative chemisorption of water. This is then followed by the energetically favourable chemisorption of hydrogen fluoride onto the clean {0001} alpha-alumina surface in a 1-2 mode via the Al-F and O-H interactions and the molecular physisorption of water onto the {0001} alpha-alumina surface. These density functional theory results are completed by the simulations of the stable surfaces of beta-alumina, the investigation into the hydroxylated {101} beta-alumina surface and the beta-AlF 3 {100} surface.
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Karlsson, Johan. "Theoretical Routes for c-BN Thin Film Growth." Doctoral thesis, Uppsala universitet, Oorganisk kemi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-191181.
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c-BN has been in focus for several years due to its interesting properties. The possibility for large area CVD is a requirement for the realization of these different properties in various applications. Unfortunately, there are at present severe problems in the CVD growth of c-BN. The purpose with this research project has been to theoretically investigate, using DFT calculations, the possibility for a layer-by-layer CVD growth of c-BN. It could be established that, PEALD, using a BF3-H2-NH3-F2 pulse cycle and a diamond substrate, is a promising method for deposition of c-BN films. The gaseous species will decompose in the plasma and form BFx, H, NHx, and F species (x = 0, 1, 2, 3). The H and F radicals will uphold the cubic structure by completely hydrogenate, or fluorinate, the growing surface. However, surface radical sites will appear during the growth process as a result of atomic H, or F, abstraction reactions. The addition of NHx growth species (x = 0, 1, 2) to B radical sites, and BFx growth species (x = 0, 1, 2) to N radical sites, will then result in a continuous growth of c-BN.
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Bernet, Thomas. "Structure microscopique et propriétés interfaciales de fluides confinés dans des matériaux poreux de diverses géométries." Thesis, Pau, 2018. http://www.theses.fr/2018PAUU3020.
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L’étude du phénomène d’adsorption peut être réalisée théoriquement dans le cadre de la physique statistique, à l’échelle microscopique, en mettant en jeu une interface entre un fluide et un solide. L’objectif de cette thèse est de proposer une modélisation moléculaire de fluides tels que le méthane, confinés dans des matériaux poreux de géométrie quelconque. Le cadre théorique est ainsi directement développé à l’échelle microscopique et ses résultats sont confrontés à ceux obtenus avec des simulations moléculaires. À l’échelle macroscopique, le formalisme théorique nous permet de retrouver des résultats expérimentaux tels que des isothermes et des chaleurs d’adsorption.Tout d’abord, nous présentons les principaux résultats de la théorie de la fonctionnelle de la densité classique (cDFT), qui permet de formuler les lois de la physique statistique à partir de la densité du fluide en chaque point de l’espace. Cette théorie permet de décrire des fluides inhomogènes, c’est-à-dire des fluides pour lesquels la densité n’est pas constante en tout point de l’espace. Nous devons également considérer une équation d’état moléculaire de référence. Nous choisissons pour cela la théorie statistique des fluides associatifs (SAFT), formulée à partir de l’énergie libre du système. Le potentiel d’interaction d’une molécule telle que le méthane est alors modélisé comme celui d’une sphère dure entourée d’une couronne attractive. Nous décrivons la sphère dure à l’aide de la théorie de la mesure fondamentale (FMT), qui utilise des densités pondérées, c’est-à-dire des fonctions exprimées en un point de l’espace, mais qui dépendent du voisinage immédiat de ce point. Les fonctions pondérées sont nécessaires pour modéliser les fluides inhomogènes confinés à l’échelle microscopique. L’étude menée à partir de la FMT nous a conduit à définir de nouvelles fonctions pondérées, permettant de décrire des fluides de sphères attractives.Dans ce nouveau cadre théorique, il est nécessaire d’utiliser des approximations dans l’écriture de la fonctionnelle d’énergie libre. Nous proposons quatre approches, avec lesquelles nous pouvons prédire la distribution de la densité du fluide dans l’espace. Ces profils étant décrits à l’échelle microscopique, nous avons réalisé des simulations moléculaires de type Monte Carlo pour en évaluer la qualité par comparaison, pour des systèmes définis à potentiel équivalent. Nous retenons alors une des nouvelles formulations décrivant le fluide inhomogène. Puis, nous nous intéressons à la modélisation du solide. De nombreuses approches utilisent des expressions analytiques des densités pondérées, ce qui ne permet d’étudier que des milieux poreux à géométrie simple et idéale. Dans le cadre de cette thèse, nous écartons ce type d’approche et nous proposons de calculer les densités pondérées à l’aide de transformées de Fourier rapides dans un espace à trois dimensions, pour une forme quelconque de pore. La conséquence numérique de cette approche est que l’on considère un espace de calcul discret. Cela demande alors d’utiliser des résultats mathématiques issus de la géométrie discrète, afin de décrire correctement les interactions entre le fluide et une surface solide discrète quelconque.Cette nouvelle combinaison entre la théorie de la fonctionnelle de la densité et la géométrie discrète permet notamment d’étudier l’adsorption de méthane dans des pores cylindriques de silice. Nous réalisons en même temps des mesures expérimentales avec ce système, en nous servant de nouveaux substrats de silice préalablement caractérisés. Nous comparons alors les isothermes et les chaleurs d’adsorption obtenues expérimentalement aux prédictions théoriques, ce qui valide l’ensemble du formalisme de l’échelle microscopique à l’échelle macroscopique, en nous servant de tous les nouveaux développements que nous présentons dans cette thèse, liés à la modélisation du fluide et à la modélisation du solideThe study of adsorption, for systems presenting an interface between a fluid and a solid, can be undertaken theoretically with the statistical physics formalism, at the microscopic scale. The objective of this PhD thesis is to propose a molecular modelling of fluids like methane, confined into porous materials of various geometry. This way, the theoretical framework is directly developed at the microscopic scale and its results are compared with molecular simulations. At the macroscopic scale, the theoretical formalism leads us to obtain the same results than experimental measurements of isotherm and heat of adsorption.First of all, the main results of the classical density functional theory (cDFT) - which gives laws of statistical physics with the fluid density in every point of the space - are presented. Inhomogeneous fluids are thus described with this theory. A molecular equation-of-state has also to be considered as a reference. The statistical associating fluid theory (SAFT), formulated with the free energy of the system has been chosen. Then, the interaction potential of a molecule such as methane is described by a hard-sphere surrounded with an attractive range. The hard-sphere is described with the fundamental-measure theory (FMT), using weighted densities, corresponding to functions defined in a point of the space, but depending on the immediate neighbourhood of this point. Weighted functions are necessary for inhomogeneous fluids modelling confined at the microscopic scale. The study undertaken from the FMT led us to define new weighted functions, allowing us to describe fluids of attractive spheres.With this new theoretical framework, it is necessary to use approximations of the free energy functional. Four different approaches are proposed allowing to predict the spatial distribution of the fluid density. Because these profiles are described at the microscopic scale, Monte Carlo molecular simulations have been performed in order to evaluate their quality by comparison, for systems defined with an equivalent potential. Thereby, one of the new formulations describing the inhomogeneous fluid has been selected for its superiority among the others. Then, special attention has been given to the modelling of the solid. Indeed, most of the existing approaches use analytical expressions of weighted densities to that extent, which limits studies to porous media with simple and ideal geometries. In our work, we exclude this kind of approaches and we propose to compute weighted densities with fast Fourier transforms in a three-dimensional space, for any pore geometry. The consequence of this approach is that a numerical discrete space is considered. This implies the use of mathematical results from discrete geometry, in order to correctly compute interactions between the fluid and any discrete solid surface.This new combination of the density functional theory and discrete geometry has allowed us to study methane adsorption into cylindrical pores of silica. To do so, experimental measurements have been performed on new silica substrates specially synthetized and characterised for this thesis. Theoretical predictions were compared with experimental isotherms and heat of adsorption. It allowed to validate the whole formalism presented in this thesis and developed both for the fluid and the solid modelling from the microscopic to the macroscopic scale
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Guhl, Hannes [Verfasser], Roberto [Akademischer Betreuer] Fornari, Norbert [Akademischer Betreuer] Koch, and Karsten [Akademischer Betreuer] Reuter. "Density functional theory study of oxygen and water adsorption on SrTiO 3 (001) / Hannes Guhl. Gutachter: Roberto Fornari ; Norbert Koch ; Karsten Reuter." Berlin : Humboldt Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2011. http://d-nb.info/1015016707/34.
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Mesta, Murat. "Adsorption Of Aromatic Molecules On Rutile Tio2(110) Surfaces." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12610928/index.pdf.
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Transition metal oxides having high dielectric constants and wide band gaps find very important and interesting technological applications in surface physics. In particular, titania is the most commonly used material in heterogeneous catalysis because of its stable and flat surfaces. Having Ti cations at different charge states within the system brings about various novel electronic properties which are mainly surface related. Adsorption of catalytically important or chemically useful molecules on titania surfaces are investigated, electronic energy bands and charge densities are calculated from first principles using the density functional theory in the GGA scheme. The comparisons with the leading theories and existing experimental data are maid.
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Danielson, Thomas Lee. "Investigation of Static and Dynamic Reaction Mechanisms at Interfaces and Surfaces Using Density Functional Theory and Kinetic Monte Carlo Simulations." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/71296.
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The following dissertation is divided into two parts. Part I deals with the modeling of helium trapping at oxide-iron interfaces in nanostructured ferritic alloys (NFAs) using density functional theory (DFT). The modelling that has been performed serves to increase the knowledge and understanding of the theory underlying the prevention of helium embrittlement in materials. Although the focus is for nuclear reactor materials, the theory can be applied to any material that may be in an environment where helium embrittlement is of concern. In addition to an improved theoretical understanding of helium embrittlement, the following DFT models will provide valuable thermodynamic and kinetic information. This information can be utilized in the development of large-scale models (such as kinetic Monte Carlo simulations) of the microstructural evolution of reactor components. Accurate modelling is an essential tool for the development of new reactor materials, as experiments for components can span decades for the lifetime of the reactor.
Part II of this dissertation deals with the development, and use of, kinetic Monte Carlo (KMC) simulations for improved efficiency in investigating catalytic chemical reactions on surfaces. An essential technique for the predictive development and discovery of catalysts relies on modelling of large-scale chemical reactions. This requires multi-scale modelling where a
common sequence of techniques would require parameterization obtained from DFT, simulation of the chemical reactions for millions of conditions using KMC (requiring millions of separate simulations), and finally simulation of the large scale reactor environment using computational fluid dynamics. The tools that have been developed will aid in the predictive discovery, development and modelling of catalysts through the use of KMC simulations. The algorithms that have been developed are versatile and thus, they can be applied to nearly any KMC simulation that would seek to overcome similar challenges as those posed by investigating catalysis (such as the need for millions of simulations, long simulation time and large discrepancies in transition probabilities).Ph. D.
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Kulkarni, Ambarish R. "Multiscale modeling of nanoporous materials for adsorptive separations." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53053.
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The detrimental effects of rising CO₂ levels on the global climate have made carbon abatement technologies one of the most widely researched areas of recent times. In this thesis, we first present a techno-economic analysis of a novel approach to directly capture CO₂ from air (Air Capture) using highly selective adsorbents. Our process modeling calculations suggest that the monetary cost of Air Capture can be reduced significantly by identifying adsorbents that have high capacities and optimum heats of adsorption. The search for the best performing material is not limited to Air Capture, but is generally applicable for any adsorption-based separation. Recently, a new class of nanoporous materials, Metal-Organic Frameworks (MOFs), have been widely studied using both experimental and computational techniques. In this thesis, we use a combined quantum chemistry and classical simulations approach to predict macroscopic properties of MOFs. Specifically, we describe a systematic procedure for developing classical force fields that accurately represent hydrocarbon interactions with the MIL-series of MOFs using Density Functional Theory (DFT) calculations. We show that this force field development technique is easily extended for screening a large number of complex open metal site MOFs for various olefin/paraffin separations. Finally, we demonstrate the capability of DFT for predicting MOF topologies by studying the effect of ligand functionalization during CuBTC synthesis. This thesis highlights the versatility and opportunities of using multiscale modeling approach that combines process modeling, classical simulations and quantum chemistry calculations to study nanoporous materials for adsorptive separations.
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Blomqvist, Andreas. "Insights into Materials Properties from Ab Initio Theory : Diffusion, Adsorption, Catalysis & Structure." Doctoral thesis, Uppsala universitet, Materialteori, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-131331.
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In this thesis, density functional theory (DFT) calculations and DFT based ab initio molecular dynamics simulations have been employed in order to gain insights into materials properties like diffusion, adsorption, catalysis, and structure. In transition metals, absorbed hydrogen atoms self-trap due to localization of metal d-electrons. The self-trapping state is shown to highly influence hydrogen diffusion in the classical over-barrier jump temperature region. Li diffusion in Li-N-H systems is investigated. The diffusion in Li3N is shown to be controlled by the concentration of vacancies. Exchanging one Li for H (Li2NH), gives a system where the diffusion no longer is dependent on the concentrations of vacancies, but instead on N-H rotations. Furthermore, exchanging another Li for H (LiNH2), results in a blockade of Li diffusion. For high-surface area hydrogen storage materials, metal organic frameworks and covalent organic frameworks, the hydrogen adsorption is studied. In metal organic frameworks, a Li-decoration is also suggested as a way to increase the hydrogen adsorption energy. In NaAlH4 doped with transition metals (TM), the hypothesis of TM-Al intermetallic alloys as the main catalytic species is supported. The source of the catalytic effect of carbon nanostructures on hydrogen desorption from NaAlH4 is shown to be the high electronegativity of the carbon nanostructures. A space-group optimized ab initio random structure search method is used to find a new ground state structure for BeC2 and MgC2. The fast change between the amorphous and the crystalline phase of GeSbTe phase-change materials is suggested to be due to the close resemblance between the local amorphous structure and the crystalline structure. Finally, we show that more than 80% of the voltage in the lead acid battery is due to relativistic effects.Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 702
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Grossman, Esther Florence. "Comparing B3LYP and its dispersion-corrected form to B97-D3 for studying adsorption and vibrational spectra in nitrogen reduction." Ohio University Honors Tutorial College / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors155628790845.
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Piccini, GiovanniMaria. "Ab initio free energies of adsorption from anharmonic vibrations." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17239.
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Die Thermodynamik von Adsorptionsvorgängen wurde mittels quantenchemischer Methoden und der statistischen Thermodynamik untersucht. Eine neue rechentechnische Methode wird vorgestellt, die den Mangel an Genauigkeit vorhandener Methoden zur Untersuchung periodischer Systeme, wie z. B. der Dichte-Funktional-Theorie, behebt, und es ermöglicht thermodynamische Funktionen mit chemischer Genauigkeit zu bestimmen. Das im Rahmen dieser Arbeit entwickelte Protokoll besteht aus verschiedenen rechentechnischen Schritten, als da wären, eine Strukturoptimierung in Normalkoordinaten anstatt in kartesischen Koordinaten, eine numerische Berechnung der harmonischen Frequenzen durch Abtasten der Potentialenergieoberfläche entlang der Normalkoordinaten und anschließender anharmonischer Korrektur. Die Normalkoordinatenoptimierung garantiert eine korrekte Relaxation der Struktur mit ausschließlich reellen harmonischen Frequenzen. Die anharmonischen Korrekturen ermöglichen eine gute Beschreibung der Schwingungsstrukturen von Systemen die durch eine besonders Flache PES gekennzeichnet sind. Gleichzeitig, wird durch die Verwendung eines QM:QM-Hybridverfahrens zur Bestimmung des elektronischen Anteils der Adsorptionsenergie eine höhere Genauigkeit in der Bestimmung der Korrelationsenergie im Vergleich zu DFT garantiert. Der elektronische Anteil der Adsorptionsenergie, sowie der Schwingungsthermische Anteil werden abschließend kombiniert um einen genauen Wert der thermodynamischen Funktionen zu erhalten.The thermodynamic of adsorption is investigated from the vibrational point of view using quantum chemical methods via statistical mechanics. Due to the lack of accuracy of the present available methods for investigating periodic systems, such as plane-wave density functional theory (DFT), a novel computational strategy is presented to overcome these limitations and bring the estimate of the thermodynamic functions within chemical accuracy limits. The protocol presented in this work consists of different computational steps, namely a structure optimization using normal mode coordinates instead of Cartesians, a numerical harmonic frequency calculation via sampling of the potential energy surface along the normal mode coordinates and the inclusion of anharmonic correction to the latter. The normal mode coordinate optimization ensures a proper relaxation of the structure and a reliable set of real harmonic frequencies while the anharmonic corrections account for a proper description of the vibrational structure of a system characterized by a very flat potential energy surface. Parallel to these calculations the electronic part of the adsorption energy is corrected using a hybrid QM:QM scheme to account the electronic correlations effects more accurately than DFT. The hybrid electronic adsorption energy and the vibrational thermal contributions obtained using anharmonic corrections are finally combined to get accurate estimate of the adsorption thermodynamic functions.
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Demiroglu, Ilker. "Ab Initio Studies Of Pentacene On Ag(111) Surfaces." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/2/12611425/index.pdf.
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In this work pentacene adsorption on both flat and stepped Ag(111) surfaces were investigated by using Density Functional Theory within Projected Augmented Wave method. On the flat Ag(111) surface favorable adsorption site for a single pentacene molecule was determined to be the bridge site with an angle of 60◦
between pentacene molecular long axis and [011] lattice direction. Potential energy surface was found to be flat, especially along lattice directions. Diffusion and rotation barriers for pentacene on this surface were found to be smaller than 40 meV indicating the possibility of a two dimensional gas phase. Calculated adsorption energies for the flat surface indicate a weak interaction between molecule and the surface indicating physisorption. On the flat surface monolayer case is found to have lower adsorption energy than the isolated case due to pentacene&
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pentacene interactions. On the stepped Ag(233) surface, close to the step edge, adsorption energy increased significantly due to the stronger interaction between pentacene molecule and low coordinated silver step atoms. On the terraces of this surface, far from step edges, however a flat potential energy surface was observed similar to the case of flat Ag(111) surface. On the stepped surface pentacene found its favorable configuration as parallel to the step with a tilt angle similar to the observed thin film phase of pentacene on Ag(111) surface. Pentacene molecule showed small distortions on stepped surface and are closer to the silver step atoms 1 Å
more than the case of flat surface, hinting a chemical interaction as well as van der Waals interactions. However on Ag(799) surface, the perpendicular orientation of the pentacene molecule to the step direction showed no strong interaction due to less matching of carbon atoms with silver step atoms.
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Oftadeh, M., M. Gholamian, and H. H. Abdallah. "Investigation of Interaction Hydrogen Sulfide with (5,0) and (5,5) Single-Wall Carbon Nanotubes by DFT Method." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35161.
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In the present study the interaction of Hydrogen Sulfide with inside and outside single-wall carbon
nanotube of (5,0) and (5,5) was investigated. This study was conducted using DFT at B3LYP/6-31G* level
of theory. Computational calculations were performed in the gaseous phase in Gaussian 09. The geometry
of all molecules under investigation was determined by optimizing all geometrical variables without any
symmetry constraints. The harmonic frequencies were computed from analytical derivatives for all species
in order to define the minimum-energy structures. The adsorption energies, the thermodynamic properties,
HOMO-LUMO energy gaps and partial charges of the interacting atoms were also studied during two rotation
kinds of H2S molecules vertical and horizontal to the main axes of nanotube.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35161
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Gallo, Erik. "Modification of the electronic structure of catalytic active transition-metal centers upon molecular adsorption : an XAS/XES study." Thesis, Rennes 1, 2013. http://www.theses.fr/2013REN1S054/document.
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Le travail de thèse "Modification of the electronic structure of catalytic active metal centres upon adsorption of molecules : a XAS and XES study" porte sur l'étude de la structure électronique des métaux de transition utilisés dans les catalyseurs par les techniques spectroscopiques d'absorption et d'émission de rayons durs (rayonnement synchrotron). Il s'agit, en particulier, d'utiliser les avancées dans les techniques spectroscopiques des rayons X pour l'étude des matériaux nanostructurés en conditions in situ. Le premier chapitre de la thèse, "X-Ray Spectroscopy: an Overview", présente brièvement les techniques spectroscopiques disponibles sur la ligne de lumière ID26 de l'Installation Européenne de Rayonnement Synchrotron (en anglais European Synchrotron Radiation Facility (ESRF), Grenoble), où toutes les mesures présentées dans ce travail ont été effectuées. Dans le deuxième chapitre, "Study of the Electronic structure of the Ti-sites in TS-1 using X-ray spectroscopy", est décrite la caractérisation électronique des centres de Ti en TS-1, qui est un important catalyseur, employé dans de nombreuses usines à travers le monde. Nous montrons que la combinaison des techniques spectroscopiques d'absorption et d'émission des rayons avec des calculs de mécanique quantique permet d'obtenir des informations importantes sur la structure électronique des centres de Ti dans des conditions in situ. Le troisième chapitre, “Identification of the Ti-Ligands in a Silica Supported Ziegler-Natta Catalyst by X-Ray Emission Spectroscopy", présente l'étude d'un catalyseur (une variante du catalyseur Ziegler-Natta), qui affiche un degré élevé/important de désordre chimique. L'utilisation de la théorie fonctionnelle de la densité des états (DFT) pour l'interprétation des données expérimentales a permis de développer des modèles possibles pour l'environnement d'un ligand Ti. Le quatrième chapitre, "Observing the dd-Excitations in CPO-27-Ni using Resonant Inelastic X-ray Scattering", conclut la partie principale de la thèse. Il présente un exemple d'utilisation de la diffusion inélastique des rayons X (RIXS) en chimie pour la détermination des excitations du champ cristallin des ions Ni dans l'oxyde de nickel et d'une cage organique autour d'un Ni métallique (CPO-27-Ni). Le chapitre explique brièvement les différentes approches théoriques qui peuvent être utilisées pour l'interprétation des caractéristiques spectrales. De plus, l'adsorption de molécules sonde, comme le CO sur les centres de Ni en CPO-27-Ni, est discutée sur la base des données expérimentales RIXS. Le dernier chapitre synthétise les résultats obtenus et indique des perspectives futures. Enfin, dans les annexes sont reportés les dispositifs expérimentaux développés dans le cadre du travail de thèse pour des mesures résolues en temps, ainsi que le curriculum vitae et les publications du candidatThe purpose of this research project was to apply advanced X-ray based spectroscopic techniques for investigating the electronic structure of transition metals within catalysts and molecular sieves under in-situ conditions. Thus, the first chapter of the thesis, "X-Ray Spectroscopy: an Overview " briefly presents the spectroscopic techniques available at ID26, beamline of the European Synchrotron Radiation Facility (Grenoble) where all the measurements reported in this work have been obtained. In the second chapter, "Study of the Electronic structure of the Ti-sites in TS-1 using hard X-ray spectroscopy", it is reported the electronic characterization of the Ti centres in titanium silicalite-1 (TS-1), that is a relevant catalyst employed in industrial plants worldwide. The chapter shows that the combination of X-ray absorption and X-ray emission spectroscopy with quantum mechanical calculations is effective to obtain important insights on the electronic structure of the Ti-centres under in-situ conditions. The third chapter entitled “Identification of the Ti-Ligands in Silica Supported Ziegler-Natta Catalyst by X- Ray Emission Spectroscopy" presents the study of a variant of the Ziegler-Natta catalyst. The chapter discusses the interpretation of the valence emission lines within the theoretical framework provided by the density functional theory (DFT) and proposes possible models for the Ti-ligand-environment. The fourth chapter, entitled "Observing the dd-Excitations in CPO-27-Ni using Resonant Inelastic X-ray Scattering", concludes the main part of the thesis. It presents the application of resonant inelastic X-ray scattering (RIXS) for obtaining the crystal field excitations of the Ni ions within nickel oxide and within a Ni- metal-organic-framework (CPO-27-Ni). The chapter briefly describes the different theoretical approaches that can be used for the interpretation of the spectral features and discusses the adsorption of probe molecules like H2O, CO and H2S on the Ni centres of CPO-27-Ni. The last chapter (Chapter five) drawn a series of conclusions concerning the performed investigations and indicates possible future research directions. In Appendix A entitled "Pump and Probe Time Resolved Experiments at ID26" it is reported the description of the experimental setup co-developed and co-realized by the candidate for time resolved experiments. The appendix also accounts for the scientific outcome of the performed pump and probe measurements. The curriculum vitae and the publications list of the candidate are respectively reported in Appendix B and C
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Vural, Kivilcim Basak. "Adsorption Of Gold Atoms On Anatase Tio2 (100)-1x1 Surface." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12610962/index.pdf.
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In this work the electronic and structural properties of anatase
TiO2 (100) surface and gold adsorption have been investigated
by using the first-principles calculations based on density
functional theory (DFT). TiO2 is a wide band-gap material and
to this effects it finds numerous applications in technology such
as, cleaning of water, self-cleaning, coating, solar cells and so
on.
Primarily, the relation between the surface energy of the anatase
(100)-1x1 phase and the TiO2-layers is examined. After
an appropriate atomic layer has been chosen according to the
stationary state of the TiO2 slab, the adsorption behavior of
the Au atom and in the different combinations are searched for both
the surface and the surface which is supported by a single Au
atom/atoms. It has been observed that a single Au atom tends to
adsorb to the surface which has an impurity of Au atom or atoms.
Although, the high metal concentration on the surface have increased
the strength of the adsorption, it is indicated that the system
gains a metallic property which is believed to cause problems in the
applications. In addition, the gold clusters of the dimer (Au2)
and the trimer (Au3) have been adsorbed on the surface and
their behavior on the surface is investigate. It is observed that
the interaction between Au atoms in the atomic cluster each other is
stronger than that of gold clusters and the surface.
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Ruiz, Lopez Victor Gonzalo [Verfasser], Alexandre [Akademischer Betreuer] Tkatchenko, Eckehard [Akademischer Betreuer] Schöll, Alexandre [Gutachter] Tkatchenko, and Eckehard [Gutachter] Schöll. "Adsorption of atoms and molecules on surfaces : density-functional theory with screened van der Waals interactions / Victor Gonzalo Ruiz Lopez ; Gutachter: Alexandre Tkatchenko, Eckehard Schöll ; Alexandre Tkatchenko, Eckehard Schöll." Berlin : Technische Universität Berlin, 2016. http://d-nb.info/1156017122/34.
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Junior, Jaldyr de Jesus Gomes Varela. "Teoria do funcional da densidade aplicada ao estudo da interação entre oxigênio molecular e nanoclusters de platina dopados com Al, Cr e V." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-06102011-144550/.
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Este trabalho apresenta um estudo aplicando a Teoria do Funcional da Densidade (DFT), utilizando o funcional B3LYP, para estudar a estrutura eletrônica de nanoclusters de platina dopados com Al, Cr e V e suas interações com oxigênio molecular. As análises das populações de Mulliken e de NBO para a interação entre O2 e Pt2, Pt-Cr e Pt-V revelaram que ocorre transferência de carga dos orbitais s e d dos metais para os orbitais p do oxigênio, resultando no preenchimento dos orbitais antiligantes da molécula de oxigênio, provocando a quebra da ligação O--O e formação de ligações hibridizadas Metal - O, com energia de dissociação da ligação O - O em 1,0 eV sobre Pt2. Sobre Pt-Cr e Pt-V, esse valor decresce para 0,56 eV e 0,20 eV, respectivamente. Os estudos da interação entre oxigênio molecular e os clusters Pt3, Pt2Al, Pt2Cr e Pt2V mostram que ocorre adsorção não dissociativa de oxigênio molecular sobre o cluster Pt3 onde observamos uma adsorção segundo o modelo de ponte enquanto que sobre os clusters Pt2Al e Pt2V ocorre adsorção dissociativa de oxigênio molecular. Por outro lado, com o cluster Pt2Cr a adsorção segue o modelo de Pauling, com o oxigênio molecular adsorvido em apenas um sítio do cluster, que foi o átomo Pt, sem a quebra da ligação O--O. Curvas de superfície de energia potencial para a dissociação de oxigênio molecular sobre Pt2Al e Pt2V mostraram um valor de aproximadamente 0,21 eV para a barreira de dissociação da ligação O--O adsorvido sobre o cluster Pt2Al e aproximadamente 0,30 eV para a barreira de dissociação da ligação O--O adsorvido sobre o cluster Pt2V. Os estudos da interação entre oxigênio molecular e os clusters Pt4, Pt3Al, Pt3Cr e Pt3V mostram que ocorre adsorção não dissociativa de oxigênio molecular sobre os clusters Pt4 e Pt3Cr onde foi observado que a adsorção segue o modelo de ponte. Por outro lado, sobre os clusters Pt3Al e Pt3V a adsorção de oxigênio molecular também seguiu o modelo ponte, com dissociação da ligação O - O. Encontramos um valor de 0,46 eV para a barreira de dissociação da ligação O--O adsorvido sobre o cluster Pt3Al e aproximadamente 0,28 eV para a barreira energética de dissociação da ligação O--O adsorvido sobre o cluster Pt3V. Os estudos para interação entre oxigênio molecular e os clusters Pt5, Pt4Al, Pt4Cr e Pt4V revelaram que ocorre adsorção dissociativa de oxigênio molecular sobre os clusters Pt4Al e Pt4V, onde observamos uma adsorção que segue o modelo de ponte enquanto que sobre o cluster Pt5 a adsorção segue o modelo de ponte sem dissociação da ligação O--O. Por outro lado, a adsorção sobre Pt4Cr segue o modelo de Pauling, com o oxigênio molecular adsorvido em apenas um sítio do cluster, sem a quebra da ligação O--O. Curvas de superfície de energia potencial mostraram um valor de aproximadamente 0,62 eV para a barreira de dissociação da ligação O--O adsorvido sobre o cluster Pt4Al e aproximadamente 0,20 eV para a barreira energética de dissociação da ligação O--O adsorvido sobre o cluster Pt4V.This work presents a study applying the Density Functional Theory (DFT) using the B3LYP functional to study the electronic structure of platinum nanoclusters doped with Al, Cr and V and their interactions with molecular oxygen. The analysis of Mulliken populations and NBO for the interaction between O2 and Pt2, Pt-Cr and Pt-V showed that charge transfer occurs orbital sed metals for the p orbitals of oxygen, resulting in the filling of the antibonding orbitals of the molecule oxygen, causing the cleavage of O-O and bond forming hybridized Metal - O, bond dissociation energy of O - O on Pt2 about 1.0 eV. On Pt-Cr and Pt-V, this value decreases to 0.56 eV and 0.20 eV, respectively. Studies of the interaction between molecular oxygen and the Pt3 clusters, Pt2Al, Pt2Cr and Pt2V show that no dissociative adsorption occurs for molecular oxygen on the cluster Pt3 where we observe a second adsorption model bridge while on clusters Pt2Al and Pt2V dissociative adsorption occurs of molecular oxygen. Moreover, with the cluster Pt2Cr adsorption follows the model of Pauling, with molecular oxygen adsorbed on only one site in the cluster, which was the Pt atom, without the cleavage of the O-O. Curves of potential energy surface for dissociation of molecular oxygen on Pt2Al and Pt2V showed a value of about 0.21 eV for the bond dissociation barrier of the O-O adsorbed on the cluster Pt2Al approximately 0.30 eV and for the barrier The bond dissociation O-O adsorbed on the cluster Pt2V. Studies of the interaction between molecular oxygen and clusters Pt4, Pt3Al, Pt3Cr and Pt3V show that no dissociative adsorption occurs for molecular oxygen on clusters Pt4 and Pt3Cr where it was observed that the adsorption follows the model of the bridge. On the other hand, on clusters Pt3Al and Pt3V adsorption of molecular oxygen also followed the model bridge, with bond dissociation O - O. We found a value of 0.46 eV for the barrier to bond dissociation to O-O adsorbed on the cluster Pt3Al and approximately 0.28 eV for bond dissociation of the O-O adsorbed on the cluster Pt3V. Studies on the interaction between molecular oxygen and clusters Pt5, Pt4Al, Pt4Cr and Pt4V revealed that occurs dissociative adsorption of molecular oxygen on clusters Pt4Al and Pt4V, where we observe an adsorption model that follows the bridge while on the adsorption cluster Pt5 follows the bridge model without the bond dissociation. Moreover, adsorption is modeled on Pt4Cr Pauling with oxygen adsorbed on only one site of the cluster, without the cleavage of the O-O. Curves of potential energy surface showed a value of about 0.62 eV for the bond dissociation barrier of the O-O adsorbed on the cluster Pt4Al and approximately 0.20 eV energy barrier for bond dissociation of the O-O adsorbed on the Pt4V cluster.
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Daramola, Oludamilola A. "Theoretical Characterization of Ammonia Oxidation Species on Platinum Clusters." Ohio University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1321547233.
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Wallin, Erik. "Alumina Thin Film Growth: Experiments and Modeling." Licentiate thesis, Linköping University, Linköping University, Plasma and Coating Physics, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-8461.
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The work presented in this thesis deals with experimental and theoretical studies related to the growth of crystalline alumina thin films. Alumina, Al2O3, is a polymorphic material utilized in a variety of applications, e.g., in the form of thin films. Many of the possibilities of alumina, and the problems associated with thin film synthesis of the material, are due to the existence of a range of different crystalline phases. Controlling the formation of the desired phase and the transformations between the polymorphs is often difficult.
In the experimental part of this work, it was shown that the thermodynamically stable alpha phase, which normally is synthesized at substrate temperatures of around 1000 °C, can be grown using reactive sputtering at a substrate temperature of 500 °C by controlling the nucleation surface. This was done by predepositing a Cr2O3 nucleation layer. Moreover, it was found that an additional requirement for the formation of the α phase is that the depositions are carried out at low enough total pressure and high enough oxygen partial pressure. Based on these observations, it was concluded that energetic bombardment, plausibly originating from energetic oxygen, is necessary for the formation of α alumina (in addition to the effect of the chromia nucleation layer). Further, the effects of impurities, especially residual water, on the growth of crystalline films were investigated by varying the partial pressure of water in the ultra high vacuum (UHV) chamber. Films deposited onto chromia nucleation layers exhibited a columnar structure and consisted of crystalline α-alumina if deposited under UHV conditions. However, as water to a partial pressure of 1x10-5 Torr was introduced, the columnar growth was interrupted. Instead, a microstructure consisting of small, equiaxed grains was formed, and the gamma-alumina content was found to increase with increasing film thickness. When gamma-alumina was formed under UHV conditions, no effects of residual water on the phase formation was observed. Moreover, the H content was found to be low (< 1 at. %) in all films. Consequently, this shows that effects of residual gases during sputter deposition of oxides can be considerable, also in cases where the impurity incorporation in the films is found to be low.
In the modeling part of the thesis, density functional theory based computational studies of adsorption of Al, O, AlO, and O2 on different alpha-alumina (0001) surfaces have been performed. The results give possible reasons for the difficulties in growing the α phase at low temperatures through the identification of several metastable adsorption sites, and also provide insights related to the effects of hydrogen on alumina growth.
Report code: LiU-TEK-LIC-2007:1.
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Arvidsson, Igor. "Theoretical Investigations of Boron Related Materials Using DFT." Doctoral thesis, Uppsala University, Department of Materials Chemistry, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7889.
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In the history of Chemistry, materials chemists have developed their ideas mainly by doing experiments in laboratories. The underlying motivation for this laboratory work has generally been pure curiosity or the ambition to find a solution to a specific problem. Minor changes in the composition or structure of a material can cause major changes in its properties. The development of powerful computers has now opened up the possibility to calculate properties of new materials using quantum mechanical methods.
The Chemistry of different boron-related materials has been evaluated in this thesis by Density Functional Theory (DFT). Cubic boron nitride (c-BN) is a most interesting material for the microelectronics and tool industry. During thin film deposition of c-BN, several problems arise which most often result in unwanted BN isomorphs. Chemical processes at the (110) and (111) surface of c-BN have been investigated in order to shed light upon some of these complex processes. Typically adsorption energies and surface reconstruction were found to differ significantly between the two surfaces.
Other materials investigated are layered transition-metal diborides (MeB2). Incorporation of transition-metal atoms into elemental boron in its most fundamental structure, ά-boron, has also been investigated. The calculations on MeB2 focused on the stability of the planar compared to the puckered structure of MeB2. Stability was investigated by calculating Density of States (DOS) and bond populations. Deviations in the cell parameters from their ideal values were also considered.
A separate project concerned reactivity of the TiB2(001) surface. Molecular and dissociated adsorption energies and adsorption geometries were calculated for H2, H2O and O2. It was concluded that the titanium surface was more reactive than the boron surface and that the adsorption energies were comparable to or stronger than other well known surface-active compounds like TiO2.
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Le, Duy. "First Principles Studies of Pattern Formations and Reactions on Catalyst Surfaces." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5390.
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This dissertation undertakes theoretical research into the adsorption, pattern formation, and reactions of atoms, molecules, and layered materials on catalyst surfaces. These investigations are carried out from first-principles calculations of electronic and geometric structures using density functional theory (DFT) for predictions and simulations at the atomic scale. The results should be useful for further study of the catalytic activities of materials and for engineering functional nanostructures. The first part of the dissertation focuses on systematic first-principles simulations of the energetic pathways of CO oxidation on the Cu2O(100) surface. These simulations show CO to oxidize spontaneously on the O-terminated Cu2O(100) surface by consuming surface oxygen atoms. The O-vacancy on Cu2O(100) then is subsequently healed by dissociative adsorption of atmospheric O2 molecules. The second part discusses the pattern formation of hydrogen on two and three layers of Co film grown on the Cu(111) surface. It is found that increasing the pressure of H2 changes the hydrogen structure from 2H-(2 x 2) to H-p(1 x 1) through an intermediate structure of 6H-(3 x 3). The third part compares the results of different ways of introducing van der Waals (vdW) interactions into DFT simulations of the adsorption and pattern formation of various molecules on certain substrates. Examinations of the physisorption of five nucleobases on graphene and of n-alkane on Pt(111) demonstrate the importance of taking vdW interactions into account, and of doing so in a way that is best suited to the particular system in question. More importantly, as the adsorption of 1,4 diaminebenzene molecules on Au(111) shows inclusion of vdW interactions is crucial for accurate simulation of the pattern formation. The final part carries out first-principles calculations of the geometric and electronic structure of the Moire pattern of a single layer of Molybdenum disulfide (MoS2) on Cu(111). The results reveal three possible stacking types. They also demonstrate that the MoS2 layer to be chemisorbed, albeit weakly, and that, while Cu surface atoms are vertically disordered, the layer itself is not strongly buckled.ID: 031001492; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Adviser: Talat S. Rahman.; Title from PDF title page (viewed July 25, 2013).; Thesis (Ph.D.)--University of Central Florida, 2012.; Includes bibliographical references (p. 128-140).
Ph.D.
Doctorate
Physics
Sciences
Physics
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Xiao, Bing. "Phase transitions, magnetism and surface adsorptions assessed by meta-GGA functionals and random phase approximation." Thesis, Temple University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3637521.
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The meta-GGA functionals and random phase approximation are tested for phase transitions and a strongly correlated transition metal oxide in this dissertation. One of the latest meta-GGA functionals is also employed to study the van der Waals bound system in surface science. Our main purpose is to reveal the performance of new exchange-correlation functionals on various properties and systems. We are also interested in seeking the possible relationship between the performance of a semilocal functional and its exchange enhancement factor.
We have studied the structural phase transitions in crystalline Si (insulator to metal), SiO2 (insulator to insulator) and Zr (metal to metal) systems, as a test of exchange energy semilocal functionals on Jacob's ladder. Our results confirm the energy-geometry delimma of GGAs in three systems. The most sophisticated non-empirical meta-generalized gradient approximations (meta-GGAs) such as TPSS (Tao-Perdew-Staroveov-Scuseria) and revTPSS (revised TPSS) give better lattice constants than PBE, but the phase transition parameters (energy difference and transition pressure) are smaller and less realistic than those from the latter GGA. However, the recent functionals of meta-GGA made simple family (MGGA_MS) behave differently to those previous meta-GGAs, predicting larger and more realistic phase transition parameters. Meanwhile, MGGA_MS also delivers the equilibrium geometry of crystalline materials similar to previous non-empirical meta-GGAs.
In contrast to semilocal functionals, the nonlocal functionals such as the range-separated hybrid functional HSE06 (Heyd-Scuseria-Ernzerhof) and non-self consistent random phase approximation (RPA) are not only able to give the accurate equilibrium geometry , but also predict the realistic phase transition parameters for Si and SiO2 systems.
The ground state of rutile-type vanadium dioxide (R-VO2) represents a great challenge to the current density functional theory. In this dissertation, we investigated the electronic structures and magnetism of R-VO2 using exchange-correlation functionals of all five rungs on Jacob's ladder. Our calculations show that all semilocal functionals (LSDA, GGAs and meta-GGAs) and hybrid functionals (HSE06) stabilize the spin-polarized states (ferromagnetic and anti-ferromagnetic states) over non-magentic state, which are completely opposite to experimental observation. Suprisingly, LSDA gives the best energetic descriptions for magnetic and non-magnetic phases of R-VO2 among semilocal functionals and HSE06. Othwerwise, RPA calculations are highly dependent on the inputs in the spin polarized case. With PBE inputs, RPA also fails, giving lower energies for spin-polarized states than for the non-magnetic phase. Meawhile, the results are reversed using LSDA inputs. From the computed equilibrium cell volume, we observe the error cancellation in the exchange-correlation hole of most semilocal functionals in the spin-polarized calculations. LSDA and RPA do not fit to this picture. By analyzing the local magnetic moments of vanadium atoms, it is found that the magnetic property predicted from meta-GGA can be related to its exchange enhancement factor.
The physisorption of a molecule on a transition metal surface is also another difficult problem in DFT because of the long-range van der Waals interactions. The recently developed MGGA_MS family of density functionals is able to capture a portion of intermediate range dispersion interactions. Therefore, we employed MGGA_MS2 to study the physisorption of CO2 on Pt (111) surface, and the results are compared to those of PBE, PBE+D2 and optB88-vdW methods. The computed binding curves comfirm that that MGGA_MS2 indeed captures the van der Waals interactions near the equilibrium binding distance, and the obtained binding distance is also in good agreement with PBE+D2 and optB88-vdW calculations. By computing the electron density difference map (EDDM), we find that the electron densities of CO2 and Pt (111) surface are strongly polarized in optB88-vdW, creating the dipole moments in two subsystems. Such effect is reduced in MGGA_MS2. For PBE, the polarization of electron density is very weak, but not negligible. The &agr; dependence in the exchange enhancement factor of a meta-GGA is the key to capture the intermediate range van der Waals interactions.
In summary, a meta-GGA functional can step out of the famous "energy-geometry dilemma" , predicting good lattice constants and phase transition parameters at the same time. With the proper construction, a meta-GGA can even capture a portion of van der Waals interactions. The RPA is usually more accurate than semilocal functionals for many ground state properties. The strongly correlated systems like R-VO2 are still a big challenge to present-day density functional theory. We will continue to seek more accurate exchange-correlation functionals.
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Soares, Carla Vieira. "Computational evaluation of MOFs for their adsorption and catalytic degradation performances with respect to chemical warfare agents." Thesis, Montpellier, 2020. http://www.theses.fr/2020MONTS015.
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Cette thèse vise à effectuer un criblage computationnel d'une grande série de structures métal-organiques (MOFs) contenant du Zr ou du Ti afin de prédire leurs performances vis-à-vis l'adsorption et dégradation des agents chimiques de guerre (ACGs). Cette étude inclut des agents neurotoxiques (Sarin et soman), agents vésicants (gaz moutarde) ainsi que leurs simulants, à savoir, le diméthyl méthylphosphonate, le diisopropyl phosphorofluoridate, le pinacolyl méthylphosphonate et le 2-chloroéthyl éthyl sulfure. Des calculs basés sur la Théorie de la Fonctionnelle de la Densité (DFT) ont été couplés à des simulations de Monte Carlo pour évaluer la capacité adsorptive, l'énergie et les sites d'adsorption préférentiels pour chaque paire MOF/ACG considérée. Ensuite, ces données ont été rationalisées afin d'établir des relations structure-propriété d'adsorption en prenant en compte des paramètres géométriques et électroniques caractéristiques des MOF, des ACGs ainsi que de leurs interactions croisées. Postérieurement, des calculs DFT ont été effectués afin d’élucider les mécanismes de dégradation des ACG et de leurs simulants sur les MOFs en analysant les principaux états intermédiaires de leurs réactions de dégradation et les énergies d'activation résultantes. Finalement, les mécanismes d'hydrolyse d'une série de MOFs à base de Ti et Zr ont été explorés par la voie des calculs DFT dans le but d'identifier les paramètres clés qui contrôlent leur stabilité sous humidité. Ces études computationnelles doivent ouvrir la voie à des nouvelles MOF avec des performances de capture/dégradation améliorées qui pourraient être appliquées comme filtres de ACGsThe present PhD thesis aims to perform a computational evaluation of a large series of Metal Organic Frameworks (MOFs) containing Zr or Ti as the metal centers for their adsorption and degradation performances with respect to chemical warfare agents: nerve agents (Sarin and Soman), vesicant agents (Sulfur Mustard) as well as their simulants, Dimethyl methylphosphonate, Diisopropyl phosphorofluoridate, Pinacolyl methylphosphonate and 2-Chloroethyl ethyl sulfide. This was achieved by combining Density Functional Theory (DFT) calculation and Monte Carlo simulations to assess the adsorption uptake, the energetics and the preferential adsorption sites for each considered MOF/CWA pair. The rationalization of the so-generated database was further achieved in order to establish structure-adsorption property relationships with the consideration of geometric and electronic descriptors characterizing MOFs, CWAs as well as CWA/MOF interactions. As a further step, DFT calculations were performed to elucidate the degradation mechanisms for CWAs and their simulants on the Ti or Zr-MOFs analyzing the main states of the degradation reaction and the resulting activation energies. Finally, the hydrolysis mechanism of a series of Zr and Ti-MOFs was explored by means of DFT calculations with the objective to identify the key parameters that control their stability under humidity. This computational work is expected to pave the way towards refined MOFs with improved capture/degradation performances to be potentially applied as CWA filters
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Wasalathilake, Kimal Chandula. "Synthesis and characterization of modified graphene for energy storage applications." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/123800/1/Kimal_Wasalathilake_Thesis.pdf.
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This thesis presents the synthesis and characterization of modified graphene materials and investigates their role in sustainable energy storage applications by using both experimental methods and density functional theory simulations. The outcomes obtained provide a better understanding of the structure-property relationship in modified graphene and its role in electrochemical process in rechargeable batteries, benefiting the development of high-performance electrode materials.
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Berro, Youssef. "Élaboration de formulations catalytiques optimisées pour la valorisation de la biomasse par une approche combinée Théorie/Expérience." Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0137.
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La valorisation de la lignine par pyrolyse produit des bio-huiles à haute teneur en oxygène. Ces bio-huiles sont valorisées par hydrodésoxygénation (HDO) pour obtenir des molécules non-oxygénées. Notre étude vise à élaborer de nouvelles catalyseurs en combinant les calculs de la théorie de la fonctionnelle de la densité (DFT) et les études expérimentales. L'HDO peut se faire suivant l'hydrogénation du cycle aromatique avant la rupture C-O (HYD) ou la rupture directe du C-O, désoxygénation directe (DDO). Le Fe/silice montre une bonne activité et sélectivité en aromatiques. Ainsi, nous développons ce type des catalyseurs afin de favoriser la voie DDO, augmenter la production d’aromatiques et limiter la consommation d’H2. Les énergies d'adsorption du phénol et de molécules inhibitrices sur les surfaces de silice, ayant différentes densités et types de silanols, ont été obtenues par DFT. Trois modes d'interaction du phénol ont été étudiés: O-perpendiculaire, π-plat et O-plat. Sur la silice amorphe, des énergies d'adsorption plus élevées ont été mises en évidence pour le mode O-plat, et une interaction spécifique de 120 kJ/mol (liaison C-Si et déformation du phénol) est observée. La compétition du CO est négligeable sur toutes les surfaces, ce qui rend la silice plus attractive que les catalyseurs sulfurés. Par conséquent, ces résultats motivent la synthèse de catalyseurs sur silice avec une densité de silanol allant de 2 à 4 OH/nm2. Des "Single Atom Catalysts SACs" de Fe/silice ont été élaborés en utilisant des tensioactifs non-ioniques/métalliques. La distribution des atomes de fer dans les micelles mixtes P123/CTAF permet la dispersion fine de ces atomes sur les mésopores de la silice. L'absence d'agrégats de fer a été confirmée par les mesures synchrotrons PDF, RMN, magnétiques, et STEM. Les calculs DFT+U ont confirmé que ces atomes sont principalement du Fe(III) à haut spin. Cette méthode augmente le nombre de sites actifs, ce qui améliore la performance catalytique. Cependant, les résultats catalytiques n’ont pas été satisfaisants à cause de la difficulté à réduire le Fe(III).Les catalyseurs Fe et bimétalliques Fe-Cu synthétisés par imprégnation ou co-précipitation avec décomposition thermale d'urée ont été testés pour l’HDO du guaiacol. Fe-Cu/SiO2 présente une meilleure performance (90% conversion, 70% sélectivité) que les catalyseurs Fe car l’incorporation de cuivre facilite la réduction du ferLignin pyrolysis produces oxygenated bio-oils with poor fuel efficiency. Hence, they are upgraded through hydrodeoxygenation (HDO) leading to the production of oxygen-free molecules and water as by-product. Our objective is to elaborate new catalysts for HDO by combining Density Functional Theory (DFT) calculations with experimental studies. HDO includes two deoxygenation routes: hydrogenation of aromatic ring before C-O cleavage (HYD) or direct C-O cleavage - Direct DeOxygenation (DDO). Fe@silica catalysts show a good activity and selectivity toward aromatics. Thus, our work focused on designing such catalysts that promote DDO in order to increase aromatics production under lower H2 pressure. The adsorption energies of phenol and inhibitors (CO and water) over silica surfaces, having various silanol densities and types, were computed by DFT. Three interaction modes were investigated: “perpendicular O-int”, “flat π-int”, and “flat O-int”. For amorphous silica, the highest adsorption energies were found for the “flat O-int” mode, and a specific interaction of 120 kJ/mol (with a C-Si bond and phenol deformation) was observed for surfaces with a silanol density between 2 and 3.3 OH/nm2. CO competitive adsorption is negligible for all silica surfaces, which make them more attractive than conventional sulfide catalysts. Hence, these results motivated the synthesis of silica-supported catalysts with a silanol density between 2 and 4 OH/nm2. Single iron atom catalysts (SACs) supported on silica were elaborated using non-ionic/metallic surfactants. Iron distribution within mixed P123/CTAF micelles, used as templates, allows the fine dispersion of those atoms within silica mesopores. The lack of iron clusters was confirmed by synchrotrons PDF, STEM mapping, magnetic and NMR measurements. DFT+U calculations confirmed that those atoms are predominately present as high spin Fe(III). This method increases the number of active sites, which improves the catalytic performance. However, the results of catalytic tests were unsatisfactory due to the difficulty of Fe(III) reduction. Metallic (Fe & Cu) and bimetallic (Fe-Cu) catalysts, synthesized by simple impregnation or through the co-precipitation method with thermal decomposition of urea, were tested for guaiacol HDO conversion. Results proved that bimetallic Fe-Cu have a better performance (90% conversion, 70% selectivity) than Fe-based catalysts since Cu incorporation facilitates the reduction of Fe(III)
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Soares, Carla Vieira. "Simulação de processos de adsorção molecular em material nanoporoso constituído por tereftalato e zircônio." Universidade Federal de Juiz de Fora, 2016. https://repositorio.ufjf.br/jspui/handle/ufjf/1819.
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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Cálculos de primeiros princípios baseados na Teoria do Funcional da Densidade (DFT) foram utilizados para investigar a adsorção de moléculas (CO2, CO, H2, CH4, N2, H2S, C4H4S, C2H4O2, C2H4O e H2O) na cavidade porosa da MOF formada por Zircônio e Tereftalato. A estrutura alvo deste trabalho denominada MIL-140A foi primeiramente validada, mostrando boa concordância com os dados espectroscópicos (Infravermelho e RMN), difratograma de raios X e parâmetros estruturais entre o modelo simulado e a estrutura experimental. Com os cálculos de estrutura eletrônica foi possível prever os sítios preferenciais para a adsorção, avaliar a força das interações adsorvente/adsorbato e determinar a ordem de seletividade para as moléculas na MIL-140A. O uso do funcional PBE aliado à correção DFT-D2 foi uma ferramenta valiosa para descrever a interação nesses sistemas. Devido ao fato das interações serem relativamente fracas, a contribuição da energia de ponto zero (EZPE) e da energia térmica (Evib(T)) são pequenas se comparadas com a contribuição das interações de dispersão. Assim, as energias vibracionais foram negligenciadas e H pôde ser aproximada para ΔEDFT. O bom acordo encontrado entre ΔEDFT e a entalpia de adsorção experimental para as moléculas (CO2, CO, CH4 e N2) comprova essa hipótese. A estabilidade da MIL-140A foi explorada mediante o cálculo da barreira de energia associada à reação de dissociação da molécula de água. O valor muito alto encontrado para a dissociação da molécula de água confirma que essa MOF se mantém estável. Os resultados demonstram que a MIL-140A pode ser um adsorvente ideal para a remoção de CO2 a partir de uma série de gases, por exemplo, gás natural, gás de síntese, biogás e gás de combustão. Além disso, a MIL-140A também pode ser utilizada na remoção do sulfeto de hidrogênio e tiofeno dos combustíveis, atuar como uma plataforma para reações envolvendo o ácido acético e reciclar o acetaldeído ejetado das indústrias.
First principle calculations based on Density Functional Theory (DFT) were used to investigate the adsorption of molecules (CO2, CO, H2, CH4, N2, H2S, C4H4S, C2H4O2, C2H4O and H2O) in a porous cavity of Zirconium terephthalate MOF. The MIL-140A was first validated by a very good agreement between the simulation and the experimental spectroscopic (Infra-red and NMR), X-ray diffraction and structural parameters of the selected MOF. The calculations of electronic structure further predicted the preferential adsorption sites, the strength of the host/guest interactions and determine the selectivity for molecules in MIL-140A. The use of the PBE XC functional integrating the DFT-D2 correction was valuable to accurately describe the interaction of those systems. Due relative weak interactions it is expected that the contribution of the zero point energies (ΔEZPE) and thermal energy contributions (ΔETE) are very small in comparison to the dispersion interactions contributions. Thus, the vibrational energies can be neglected and thus ΔH can be approximated to ΔEDFT. A very good agreement between ΔEDFT and the experimental adsorption enthalpy determined for the molecules (CO2, CO, CH4 e N2) confirms this assumption. The water stability of the MIL-140A was explored through the activation barrier associated to the dissociative chemisorption of water. Its high value confirms the very good water stability of this MOF. These results demonstrate that the MIL-140A could act as an ideal adsorvent for the removal of CO2 from a series of gases (e.g. natural gas, syngas, biogas and flue gas). Furthermore the MIL-140A can be able to remove hydrogen sulfide and thiophene from the fuels, act as a platform for reactions with acid acetic and recycle the acetaldehyde ejected from the factories.
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Jauris, Iuri Medeiros. "ADSORÇÃO DE CORANTES EM NANOTUBOS DE CARBONO: UMA ABORDAGEM DE PRIMEIROS PRINCÍPIOS." Universidade Franciscana, 2012. http://tede.universidadefranciscana.edu.br:8080/handle/UFN-BDTD/195.
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Dyes are organic compounds used to color or bring shine to other substances, being widely used by the cosmetic industries, pulp, textiles, and many others. However, the complex aromatic structure of these compounds makes them highly stable. In addition, some types of dyes could be toxic to humans or even carcinogenic. Thus, treatment of effluent water contaminated with these dyes is mandatory. Fortunately some recent studies have reported the ability of Carbon Nanotubes (CNTs) to act as adsorbent material for treating aqueous effluents contaminated with dyes. Nevertheless, to the best of our knowledge, so far, none theoretical study focusing mainly in the interaction of CNTs and dyes is available. From this perspective, in this work we have used ab initio simulations based on the densityfunctional theory and implemented on the SIESTA code to evaluate the interaction of tree dyes (Acridine Orange, Alizarin Red S, Methylene blue) and the Anthracene molecule with the pristine (5,5), (8,0) Single Wall Carbon Nanotubes (SWCNTs). Also we have investigate the interaction of those molecules with the pristine (5,5), (8,0) 1-vacancy-SWCNTs. Moreover, to appraise the effects in dye-SWCNT interaction due to SWCNT diameter, we compared the configurations dyes-pristine SWCNTs (5,5); (8,0) with dyes-pristine SWCNTs (16,0); (25,0). Our results show that, in general, the main configurations exhibit an average binding energy around (0.75 eV ≈ 72.36 kJ / mol), characteristic of physical adsorption. This feature could facilitate the eliminations of these dyes after being adsorbed by SWCNTs, enabling the reuse of SWCNTs. Also, the SWCNTs with vacancy have binding energies lower than the CNTs without vacancy, except to the case of methylene blue-SWCNTs. Further, the dyes SWCNTs (5,5) present binding energy greater than dyes SWCNTs (8,0). In most, was not found significant change in molecular structure and electronic character of SWCNTs. Furthermore, dyes-pristine SWCNTs (5,5) and (8,0) present lower binding energy in comparison with dyes-pristine SWCNTs (16,0) and (25,0).
Corantes são compostos orgânicos utilizados para dar cor e/ou conferir brilho a outras substâncias, sendo amplamente empregados nas indústrias de cosméticos, celulose, têxteis, alimentos dentre outros. No entanto, o complexo aromático presente na estrutura destes compostos torna-os altamente estáveis. Além disso, alguns tipos de corantes podem ser tóxicos ou até mesmo carcinogênicos, assim, o tratamento de efluentes aquáticos contaminados por tais compostos é imprescindível. Para tanto, alguns estudos recentes têm relatado a capacidade dos nanotubos de carbono (NTCs) de atuarem como material adsorvente para o tratamento de efluentes aquosos contaminados com tais corantes. Todavia, até o momento, não foi reportado na literatura nenhum estudo teórico com enfoque principalmente na interação entre os nanotubos de carbono e os corantes. Desse modo, a partir desta perspectiva, para avaliar a interação dos corantes: laranja de acridina (LA), vermelho de alizarina S (VAS) e azul de metileno (AM), bem como a molécula de antraceno (AN), com os nanotubos de carbono de parede simples, NTCPS (5,5), (8,0), puros, fez-se uso de cálculos ab initio, baseados na teoria do funcional da densidade, e implementados pelo código SIESTA. Além disso, também se investigou a interação destes corantes com os NTCPS (5,5), (8,0) com uma vacância. Da mesma forma, estudou-se a interação dos NTCPS (16,0) e (25,0) com os corantes LA, VAS e AM, além da molécula de AM, a fim de avaliar a influência do diâmetro dos nanotubos de carbono na interação com tais corantes. Nossos resultados mostram que as configurações principais exibem energia de ligação média em torno de (0,75 eV ≈ 72,36 kJ / mol), características de processos de adsorção física. Energias dessa ordem podem facilitar a dessorção destes corantes, permitindo, assim, a reutilização dos NTCPS. Além disso, na interação corantes-NTCPS, para a maioria das configurações, os NTCPS com uma vacância apresentaram energias de ligação menores do que os NTCPS sem vacância, e os NTCPS (5,5) apresentaram energia de ligação maior do que para os NTCPS (8,0). Mais ainda, não foram encontradas alterações significativas na estrutura molecular e caráter eletrônico dos NTCPS (5,5) e (8,0). Por fim, ressalta-se que, para todas as configurações, a interação corante-NTCPS (8,0) apresentou energia de ligação menor do que a interação corante-NTCPS (16,0) e corante-NTCPS (25,0).
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Mikhail, Hanna Degani. "Análise teórica da superfície Si(111)-(7x7)." Universidade Federal de Uberlândia, 2007. https://repositorio.ufu.br/handle/123456789/15681.
Full textAbstract:
In this work, wecarry out theoretical study of the silicon surface reconstruction (7x7)
grown in the [111] direction, denoted by Si(111) (7x7), using the Density Functional
Theory formalism, within the Local Density Approximation (LDA) for the exchange
correlation term. The interaction with the valence electrons and the core ion (nucleus
more core electrons) was described by norm conserving, non local pseudopotential
approach, compatible with the LDA. The one electron Kohn Sham equations was
solved self consistently, by expanding the one electron functions in terms of linear
combination of numerical atomic orbitals. All the calculations were realized using the
Siesta computational code.
Using the clean surface reconstruction model of Si(111) (7x7), propose by Takayanagi
et al.[1, 2], we modeled the surface as a slab, in which the (7x7) unitary cell
contained 200 Si atoms distributed in one adatom layer (Si atoms on the topmost layer)
and the other four layers, with 49 H atoms used for saturate the dangling bonds of the
most internal layer of the slab. The structural analysis of the Si(111) (7x7) reconstructed
surface and the electronic structure analysis showed a good agreement with both the
experimental and theoretical results disposable, reproducing correctly the band structure,
the surface levels and the metallic character of this surface. The obtained energy
per surface atom was 1,132 eV with respect to the bulk energy. It was performed the
study of the vacancy energy formation of adatoms on this surface. We find an average
value of 1,2 eV of a single vacancy formation of adatom the Si(111) (7x7) surface. The
analysis of the energy bands made possible to identify the electronic states due to the
adatoms dangling bonds.
As a first application of the obtained results to the Si(111) (7x7) clean surface, we
investigated the possible states of the physisorption of the chlorobenzene molecules
on specific sites on the Si(111) (7x7) surface. This study showed that chlorobenzene
molecules interact with the surface for distances around 3,0 Å from the adatoms. We
also inferred that the triangular faulted subunit sites are energetically most favorable
to the adsorption than the correspondent triangular unfaulted subunit sites.
We plotted the adsorption energy curve of the chlorobenzene on the corner adatom
at the triangular faulted unitary cell (7x7). The equilibrium distance and the adsorption
energy obtained was 3,005 Å and 0,161 eV, respectively. The magnitude of this
interaction corresponds to a physics adsorption of the chlorobenzene molecule on the
Si(111) (7x7) surface.Neste trabalho, realizamos o estudo teórico da reconstrução (7x7) da superfície de Silício crescida na direção [111], denotada por Si(111) (7x7), utilizando para isto o formalismo da Teoria do Funcional da Densidade, com a Aproximação da Densidade Local (LDA - LocalDensityApproximation) para o termo de troca correlação. A interação entre os elétrons de valência e o íon de caroço (núcleo mais os elétrons de caroço) foi descrita por meio da Teoria dos Pseudopotenciais não locais de norma conservada, compativel com a LDA. As equações de Kohn Sham de um elétron foram resolvidas autoconsistentemente, expandindo as funções de um elétronemtermos de combinação linear de orbitais atômico numéricos, com base double . Todos os cálculos foram realizados utilizando o código computacional Siesta. Utilizando o modelo de reconstrução da superfície livre de Si(111) (7x7), proposto por Takayanagi et al.[1, 2], modelamos a superfície como um slab, cuja célula unitária (7x7) contém 200 átomos de Si distribuidos em uma camada de adatoms (átomos de Si adsorvidos sobre a superfície propriamente dita) e quatro outras camadas, além dos 49 átomos de H usados para saturar as ligações pendentes da camada mais interna ao material. A análise estrutural da superfície reconstruída Si(111) (7x7) e a análise da estrutura eletrônica mostrou ótima concordância tanto com trabalhos experimentais quanto teóricos, reproduzindo corretamente a estrutura de bandas, os níveis de superfície e o caráter metálico desta superfície. A energia obtida em nosso cálculo por átomo da superfície, com relação à energia bulk, foi de 1,132 eV. Foi feito o estudo da energia de formação de vacâncias do tipo adatom. Encontramos um valor médio de 1,2 eV para a formação de uma única vacância do tipo adatom na superfície Si(111) (7x7). A análise da estrutura de bandas do sistema com vacância possibilitou identificar os estados eletrônicos devido às ligações pendentes dos adatoms. Como uma primeira aplicação dos resultados obtidos para a superfície livre de Si(111) (7x7), investigamos possíveis estados de fisiossorção de moléculas de clorobenzeno sobre sítios específicos sobre a superfície de Si(111) (7x7). Este estudo mostrou que as moléculas de clorobenzeno interagem com a superfície para distâncias de aproximadamente 3,0 Å dos adatoms. Também inferimos que sítios da subunidade triangular faulted são mais favoráveis à adsorção do que sítios correspondentes sobre a subunidade triangula unfaulted. Levantamos a curva da energia de adsorção do clorobenzeno sobre o adatom de canto da subunidade triangular faulted da célula unitária (7x7). A distância de equilíbrio e a energia de adsorção obtidas foram 3,005 Å e 0,161 eV, respectivamente. A ordem de grandeza desta interação corresponde a uma adsorção física da molécula de clorobenzeno sobre a superfície Si(111) (7x7).
Mestre em Física
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Houwaart, Torsten. "Cobalt porphyrins on coinage metal surfaces - adsorption and template properties." Thesis, Lyon, École normale supérieure, 2014. http://www.theses.fr/2014ENSL0927.
Full textAbstract:
Cette thèse est une étude théorique sur la interface de porphyrine de cobalt avec des surfaces métalliques avec le code VASP DFT. Le cadre DFT nécessaire a été introduit dans le chapitre 1. La structure de la jBardeen, une programme ecrit en Java, pour la simulation de la STM est expliqué dans le chapitre 2 et le code source est jointe en annexe. Une étude de l'adsorption de CoTPP sur les surfaces métalliques a été entrepris dans le chapitre 3. Différents paramètres de calcul ont été évalués: Le site d'adsorption et de la géométrie à la fois la molécule et la surface ont été étudiés par rapport à la xc-fonctionnel et correction de la dispersion utilisée. Une adsorption site le plus stable est identifié. Par conséquent, ce site plus stable a été étudiée pour sa structure électronique. Calculés images STM avec le code jBardeen ont été comparés avec une experimentation de CoTPP Cu sur une surface (111) avec une couverture sous monocouche. Dans le chapitre 4, un adatome Fe a été présenté à la CoTPP sur Ag système (111). Trois sites de liaison symétrique différentes pour l'atome Fe ont été identifiés sur le macrocycle, marqué les , bi-, brd- et bru-positions. Un moment magnétique pouvait être attestée qui a été principalement situé sur l'atome Fe. Voies possibles entre les quatre, symétriquement équivalentes, sites bi- ont été étudiées avec des méthodes différentes. Simples calculs dans le vacuum et calculs de la “Nudged Elastic Band” (NEB) de l'ensemble du système a révélé une hauteur de barrière légèrement au-dessus de 0,2 eV allant de position bi à la posititon brd. Une analyse de vibration a montré que la commutation de l'atome Fe est susceptible, lorsqu'il est perturbé hors d'équilibre dans les positions brd et bruThis thesis is a theoretical study on the cobalt porphyrin - coinage metal surface interface with the DFT code VASP. The necessary DFT framework has been introduced in chapter 1. The structure of the Java program jBardeen for STM simulation is explained in chapter 2 and the source code is attached as Appendix. A study of the adsorption of CoTPP on coinage metal surfaces has been undertaken in chapter 3. Different parameters of the calculation have been evaluated: the adsorption site and the geometry of both the molecule and surface have been investigated with respect to the xc-functional and dispersion correction used. A most stable adsorption site -bridge down- is identified. Consequently, this most stable site was investigated for its electronic structure. Calculated STM images with the jBardeen code were compared with an experiment of CoTPP on a Cu(111) surface with sub monolayer coverage. In chapter 4 an Fe adatom was introduced to the CoTPP on Ag(111) system. Three symmetrically different binding sites for the Fe atom were identified on the macrocycle, labelled the bi-, brd- and bru-positions for bisector, bridge down and bridge up respectively. A magnetic moment could be evidenced which was mainly located on the Fe atom. Possible pathways between the four symmetrically equivalent bisector sites were investigated with different methods. Single point calculations in vacuum and Nudged Elastic Band (NEB) of the whole system revealed a barrier height of slightly above 0.2 eV going from bi- to the brd-position. A vibrational analysis showed that switching of the Fe atom is likely, when perturbed out of equilibrium in the brd- and bru- positions
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Lourenço, Mirtha Alejandra de Oliveira. "Tuning functionalized periodic mesoporous organosilicas for CO2/CH." Doctoral thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/21817.
Full textAbstract:
Doutoramento em Ciência e Engenharia de MateriaisEsta tese de doutoramento teve como principal objetivo a conceção de novas organossílicas mesoporosas periódicas (PMOs) para aplicação na separação de misturas gasosas de dióxido de carbono e metano. Materiais PMOs, com grupos fenileno e bifenileno bissililados, foram modificados por introdução de grupos funcionais amina, utilizando uma das seguintes metodologias: i) reação de co-condensação; ii) pós-modificação da ponte orgânica; iii) "grafting". O tamanho dos poros das PMOs funcionalizadas e não funcionalizadas foi definido pelo tamanho da cadeia alquilada da molécula molde (surfactante) utilizada na síntese do material poroso. Estudou-se o efeito do diâmetro dos poros na separação de CO2/CH4. Investigou-se também estratégias alternativas para modificar as propriedades físico-químicas dos materiais através de reações de superfície utilizando irradiação de micro-ondas; deposição de camada atómica (ALD) de óxido de alumínio; e carbonização dos materiais em atmosfera inerte. A investigação experimental foi efectuada em paralelo com estudos computacionais. Realizou-se um estudo de simulação molecular recorrendo ao método de DFT, e usando um arranjo regular de grupos fenileno-sílica, para determinar as características ideais dos materiais para promover a separação de metano do dióxido de carbono em misturas destes gases. Foi utilizado um modelo simples, obtido pela repetição de uma célula unitária com 3 anéis fenileno, para simular a parede dos materiais PMOs e desta forma selecionar e avaliar as interações entre os gases e os grupos funcionais presentes na superfície dos materiais. A tendência do rácio entre energias de interação entre a estrutura da parede do fenileno - PMO e as moléculas de CO2 e de CH4 foi concordante com os rácios das constantes de Henry obtidos pela técnica de adsorção. Demonstrou-se uma boa sinergia entre tarefas experimentais e computacionais, o que permite a otimização de recursos, evitando a síntese desnecessária de materiais que se antecipem serem pouco eficazes para o processo de separação de misturas gasosas CO2 e CH4. Assim, a abordagem seguida nesta tese para alcançar adsorventes eficazes foi baseada numa conjugação interdisciplinar envolvendo troca de informação entre as tarefas de síntese, modelação computacional e adsorção.
The main objective of this PhD Thesis was the design of periodic mesoporous organosilicas (PMOs) for applications in carbon dioxide and methane separation. Novel PMOs were prepared by the modification of phenylene and biphenylene PMO materials with different amine functionalities through one of the three following synthetic strategies: i) co-condensation reaction; ii) organic bridge post-modification; or/and iii) grafting. The pore size of both functionalized and non-functionalized phenylene PMOs was regulated by the size of the alkyl-chain in the surfactant template. Materials with different pore sizes were used to understand the influence of the pore diameter on the CO2/CH4 separation. Additionally, it was aimed to explore alternative strategies to modify the physical-chemical properties of the materials such as microwave-assisted functionalization; atomic layer deposition (ALD) of aluminum oxide at the PMO surfaces; and carbonization of the PMO materials. The experimental research was performed in parallel with computational studies. A molecular simulation study, using the DFT method and a regular arrangement of phenylene-silica groups, of the ideal characteristics of the adsorbent materials, for CO2/CH4 separation was performed. It was used a simple model of the wall of the PMO materials obtained by the repetition of a unit cell with 3 phenylene rings, to select and evaluate interactions between gases and functional groups in the surface of the materials. The tendency between the ratio of the interaction energies between the wall structure of the phenylene-PMO and the CO2 and CH4 molecules was in good agreement with the ratio of the Henry constants achieved by the adsorption technique. Therefore, a good synergy between experimental and computational tasks was implemented to optimize the resources, avoiding the synthesis of ineffective materials. Thus, the strategy of this PhD Thesis to achieve effective adsorbents was based on an interdisciplinary approach and on the ability to link and interchange information between synthetic, computer modeling and adsorption experiments
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Carvalho, Arivaldo Cutrim. "Interação de glicina com grafeno: uma abordagem de modelagem molecular." Universidade Federal do Maranhão, 2010. http://tedebc.ufma.br:8080/jspui/handle/tede/718.
Full textAbstract:
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With the aim of the development of new nanodevices, there is great interest in understand the electronic properties of nanostructured materials. Above all, how to modify the electronic properties of nanostructures already well known in a controlled manner. With this goal, many methodologies and experiments has been developed. We studied the an entirely through computer simulation atomistic interaction of amino glycine with the surface of graphene using two methods, classical and quantum, for both modules use Materials Studio (Accelrys), and the Forcit Dmol3 states that are Art in atomistic simulations. From the classical point of view, we used force fields universal to describe the interactions, and the quantum point of view, the method of density functional. The methodology consisted basically realize a scan with glycine in different orientations on the surface of the graphene sheet grid in a considerable build a 3D map of potential interaction that enables us to accurately define where are enough sites and orientations of the amino acid glycine to more energetically favorable for adsorption. From the selection of the best candidates obtained from calculations in classical mechanics, we performed electronic structure calculations using the method DFT (Density Functional Theory) to estimate the binding energy and in that regime adsorption occurs. In addition, we obtained the electron density of the system and did Mulliken population analysis as well.
Com a finalidade do desenvolvimentos de novos nanodispositivos, há um grande interesse em conhecer as propriedades eletrônicas de materias nanoestruturados. Sobretudo, como modificar as propriedades eletrônicas de nanoestruturas já bem conhecidas de forma controlada. Com este objetivo, muitas metodologias e experimentos tem sido desenvolvidos. Estudou-se de forma inteiramente atomística através de simulação computacional a interação do aminoácido glicina com a superfície do grafeno utilizando dois métodos , clássico e quântico, para tanto utilizamos os módulos do Materials Studio (Accelrys), o Forcite e o Dmol3 que são estados de arte em simulações atomísticas. Do ponto de vista clássico, utilizou-se campos de força universal para descrever as interações; e do ponto de vista quântico, utilizamos o método do funcional da densidade. A metodologia consistiu basicamente em realizarmos um "scan"com a glicina em diversas orientações sobre a superfície da folha de grafeno num grid considerável, construímos uma mapa 3D do potencial de interação que nos possibilita conhecer com precisão suficiente onde são os sítios e as orientações do aminoácido glicina que mais favoráveis energeticamente para a adsorção. A partir da seleção dos melhores candidatos obtidos através dos cálculos de mecânica clássica, realizamos cálculos de estrutura eletrônica utilizando o método DFT (Density Functional Theory) a fim de estimar a energia de ligação e em que regime ocorre a adsorção. Além disso, nós obtivemos a densidade eletrônica do sistema e fizemos uma análise populacional de Mulliken também.
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Machado, Fernando Machado. "Nanotubos de carbono como nanoadsorventes na remoção de corantes sintéticos de soluções aquosos : um estudo experimental e teórico." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/49309.
Full textAbstract:
Este trabalho teve como objetivo investigar a adsorção de corantes têxteis (Vermelho Reativo 194 e Azul de Prociona MX-R) em nanotubos de carbono (NTC) em meio aquoso. Para tanto, empregou-se nanotubos de carbono de paredes múltiplas (NTCPM) e carvão ativo (CA) em pó, ambos comerciais, na remoção do corante têxtil Vermelho Reativo 194 e nanotubos de carbono de parede simples (NTCPS) e NTCPM na remoção do corante têxtil Azul de Prociona MX-R. Os NTCPS foram sintetizados utilizando a técnica de deposição química de vapor catalisada. Os adsorventes foram caracterizados por espectroscopia no infravermelho e Raman, isotermas de adsorção/dessorção de N2 e microscopia eletrônica de varredura e de transmissão. Os efeitos do pH, tempo de agitação e da temperatura na capacidade de adsorção foram investigados. O tempo de contato para obter equilíbrio a 298 K foi fixado em uma hora para o caso onde foi empregado o corante Vermelho Reativo 194 e três horas para o caso onde foi empregado o Azul de Prociona MX-R. A região de pH ácido (pH 2,0) foi favorável para as adsorções de ambos corantes. A energia de ativação do processo de adsorção foi avaliada nas temperaturas entre 298-323 K para os NTCPM e CA, na adsorção do corante Vermelho Reativo 194. O modelo cinético de ordem fracionária de Avrami foi o que melhor se ajustou aos dados experimentais do corante Vermelho Reativo 194 em comparação com os modelos cinéticos de adsorção de pseudo-primeira ordem e pseudo-segunda ordem. Por outro lado, o modelo cinético de ordem geral foi o que melhor se ajustou aos dados experimentais do corante Azul de Prociano MX-R, em comparação aos modelos de pseudo-primeira ordem e pseudo-segunda ordem. Tanto para o corante Vermelho Reativo 194, quanto para o corante Azul de Prociona MX-R, os dados de equilíbrio obedeceram ao modelo de isoterma de Liu. O cálculo dos parâmetros termodinâmicos de adsorção indicou que a adsorção de ambos ocorre de forma endotérmica, espontânea e favorável para todas as temperaturas investigadas. Adicionalmente, a magnitude da entalpia indica que a adsorção para os dois corantes se dá através de interação eletrostática. Isso pode ser confirmado por cálculos ab initio, baseados na teoria do funcional da densidade, implementados no código SIESTA, para a adsorção do Azul de Prociona MX-R e um NTCPS (8,0).This work aimed to investigate the adsorption of textile dyes (Reactive Red M-2BE and Reactive Blue 4) on carbon nanotubes (CNT). To this purpose, multi-walled carbon nanotubes (MWCNT) and powdered activated carbon (AC), both commercial, were used in removal of textile dye Reactive Red M-2BE and single-wall carbon nanotubes (SWCNT) and MWCNT in the removal of textile dye Reactive Blue 4. The SWCNT were synthesized by catalytical chemical vapour deposition. The adsorbents were characterised by infrared and Raman spectroscopy, N2 adsorption/desorption isotherms and scanning and transmission electron microscopy. The effects of pH, shaking time and temperature on adsorption capacity were studied. The contact time to obtain equilibrium at 298 K was fixed at 1 hour for the case where the Reactive Red M-2BE dye was used and 3 hours for the case where the dye was used Reactive Blue 4. In the acidic pH region (pH 2.0), the adsorption of the both dyes were favourable. The activation energy of the adsorption process was evaluated from 298 to 323 K for MWCNT and AC, in the adsorption of the Reactive Red M-2BE dye. The Avrami fractional-order kinetic model provided the best fit to the experimental data of the Reactive Red M-2BE dye compared with pseudo-first-order or pseudo-second-order kinetic adsorption models. On the other hand, the general order kinetic model provided the best fit to the experimental data of the Reactive Blue 4 dye, compared with pseudo-first order and pseudo-second order kinetic adsorption models. For both the Reactive Red M-2BE and the Reactive Blue 4 dyes, the equilibrium data were best fitted to the Liu isotherm model. The calculation of the thermodynamic parameters of adsorption indicated that adsorption of both dyes by adsorbents occurs so endothermic, spontaneous and favorable for all temperatures studied. Additionally, the magnitude of enthalpy indicates that the adsorption process for both dyes occurs through electrostatic interaction. This can be confirmed by ab initio calculations based on density functional theory, implemented in the SIESTA code, for the adsorption of Reactive Blue 4 textile dye and a SWCNT (8.0).
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Oliveira, Joao Batista de. "Estudo das propriedades eletrônicas, energéticas e estruturais de moléculas adsorvidas em estruturas 1D e 2D de SiC." Universidade Federal de Uberlândia, 2014. https://repositorio.ufu.br/handle/123456789/15613.
Full textAbstract:
In this work, we performed an ab initio study of interaction between several molecules
with SiC nanotubes and SiC Sheets, with focus on benzene molecule. performed too a
study the mechanical and electronic properties of SiC nanowires(SiCNWs).
For study the interaction of molecules with SiCNTs and SiCSheets, we considered two
possibilities, (1) molecules adsorbed on SiCNT/SiCSheet surface, and (2) molecules encapsulated
by SiCNT. We have considered several geometries for adsorption and dierent
nanotube chiralities. For study of mechanical and electronics properties of SiCNWs, we
considered 3C-, 2H, 4H and 6H-SiCNW, analyzing the eects of the diameter on these
properties.
All calculations were performed by using the Density Funcional Theory, using de the
Local Density Approximation (LDA). The electron-ion interaction was describe by using
norm-conserving pseudopotentials.
For the benzene adsorption on the SiCNT, we nd an exothermic process, with binding
energies between 0.3 and 0.4 eV/molecule, and for benzene encapsuladed we nd
binding energies of 0.6 eV/molecule, revealing a preference for the benzene encapsulated
systems. For both cases, we verify that there are not chemical bonds at the benzene-
SiCNT/SiCSheet interface, and the interaction of benzene molecule with nanotube and
Sheet is mediated by pi stacking interactions, similar to the benzene-CNT systems.
For both cases, we verify that SiCNTs are more reactive than the carbon nanotube (CNTs)
For nanowires study, our results show that all nanowires investigated exhibit direct
band gaps, in contrast with the indirect band gap observed in Bulk SiC. The study of
eect of unixial stress on the electronic properties of nanowires, reveal that band-gap
dependence on the strain is dierent for each nanowire type.
For the mechanicals properties, our results revels that Youngs moduli of nanowires
show strong dependece on the diameters, and the 2H-SiCNWs are stier than than other
nanowires with similar diameter. The values for Youngs moduli of dierent SiCNWs,
revels that they are more stifer than nanowires of other elements, for example Si, InAs
and Ge.Neste trabalho, nós realizamos um estudo ab initio da interação entre diversas moléculas com nanotubos de SiC e folhas de SiC(SiCfolhas), com foco na molécula de benzeno. Realizamos também um estudo das propriedades mecânicas e eletrônicas de nanoos de SiC(SiCNWs). Para estudar a interação de moléculas com SiCNTs e SiCSfolhas, consideramos duas possibilidades, (1) moléculas adsorvidas na superfície do SiCNT/SiCfolha, (2) moléculas encapsuladas em SiCNTs. Nós consideramos várias geometrias para a adsorção e nanotubos de diferentes quiralidades. Para o estudo das propriedades mecânicas e eletrônicas dos SiCNWs, consideramos 3C-, 2H-, 4H- e 6H-SiCNWs, analisando o efeito do diâmetro nestas propriedades. Todos os cálculos foram feitos com a utilização da Teoria do Funcional da Densidade, com a Aproximação da Densidade Local(LDA). A interacção elétron-íon foi descrita com a utilização de pseudopotencias de norma conservada. Para a adsorção do benzeno em SiCNTs, nós observamos um processo exotêrmico, com energias de ligação entre 0.3 e 0.4 eV/molécula, para o encapsulamento obtivemos energias de aproximadamente 0.6 eV/molécula, o que mostra uma prefêrencia pelo encapsulamento. Nós observamos que não ocorre a formação de ligações químicas na interface benzeno- SiCNT/SiCfolha, e a interação da molécula de benzeno com o nanotubo e a folha ocorre via interação - stacking, similar ao que ocorre para o sistema benzeno-CNT. Para ambos os casos nós vericamos que os SiCNTs são mais reativos do que os nanotubos de carbono (CNTs). Para o estudo dos nanoos, nossos resultados mostram que todos os nanoos investigados exibem gap direto, em contraste com o que se observa nos SiC Bulk. O estudo dos efeitos do stress uniaxial nas propriedades eletrônicas dos nanoos, revela que a dependencia do gap de energia com o strees/strain é diferente para cada nanoo. Para as propriedades mecânicas, nossos resultados revelam que o módulo de Young dos os mostra uma forte depêndencia com o diâmetro, e o 2H-SiCNW é mais duro do que outros nanoos com diâmetros similares. Os valores encontrados para o módulo de Young dos diferentes SiCNWs, revelam também que eles são mais duros do que nanoos formados por outros elementos como Si, Ge e InAs.
Doutor em Física
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Schweigert, Igor Vitalyevich. "Ab initio Density Functional Theory." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0011614.
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Laming, Gregory John. "Density functional theory for molecules." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336907.
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