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1
Lin, Xufeng. « Density functional theory studies of selected transition metals catalyzed C-C and C-N bond formation reactions ». Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B39359645.
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Sheffield, Carolyn Evans. « Time-Resolved Infrared Spectroscopy and Density Functional Theory Study of Weak Interactions of Metal Carbonyls and Organic Solvents ». Diss., CLICK HERE for online access, 2010. http://contentdm.lib.byu.edu/ETD/image/etd3389.pdf.
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Lin, Xufeng, et 林旭鋒. « Density functional theory studies of selected transition metals catalyzed C-C and C-N bond formation reactions ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39359645.
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BABY, ANU. « Interfacce ibride : adsorbimento di molecole aromatiche sui metalli ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2016. http://hdl.handle.net/10281/101818.
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This thesis presents density functional theory (DFT) studies of the adsorption of aromatic molecules on metals. These hybrid interfaces are found at the electrical contacts in the organic electronic devices. Understanding the precise electronic structure including the energy alignment between the Fermi level of the metal and the HOMO/LUMO states of the molecule is essential as it influences the carrier injection across the interface, which in turn affects the overall performance of these devices. The topography of the first layer of adsorbates is very important as it drives the orientation of the subsequent growing layers. In this respect I have studied by DFT including van der Waals interactions the structural, electronic, and spectroscopic properties of pentacene adsorbed on the Al(001) surface in collaboration with experimentalists who measured the X-ray photoemission spectra (XPS), the near-edge X-ray absorption fine structure (NEXAFS), and the surface charge maps by scanning tunneling microscopy (STM). We find a major change of the molecular backbone resulting in a peculiar V- shape bending, due to the direct anchoring of the two central carbons atop the two Al atoms underneath. In the most stable adsorption configuration, pentacene is oriented with the long axis parallel to the substrate [110] direction, where such anchoring is favored by optimally matched interatomic distances which results in filling of the LUMO. Next I have investigated computationally K doping of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) adsorbed on Ag(111), during my secondment at the Graz University of Technology, Austria. In fact another key parameter to be tuned as far as the device performance is concerned is the number of charge carriers which can be improved by doping. Alkali metal atoms are frequently used for simple yet efficient n-type doping of organic semiconductors. The incorporation of dopants from the gas phase into molecular crystal structures needs to be controlled and well understood in order to optimize the electronic properties (charge carrier density and mobility) of the target material. We found that K doping induces distinct stoichiometry-dependent structural reordering processes, resulting in highly ordered and large KxPTCDA domains. The emerging structures were found to be stable for stoichiometries x = 2 and 4. These were analyzed by an experimental group that used low temperature STM, scanning tunneling hydrogen microscopy (STHM), and low-energy electron diffraction (LEED). The DFT calculations have proven essential for a correct interpretation of the experimental ST[H]M data. In this way we have determined the K atom positions, located in the vicinity of the oxygen atoms of the PTCDA molecules with sub-Ångstrom precision. Our calculations have shown that the K atoms eventually lose their electrons to PTCDA and the Ag substrate thereby filling the LUMO of the former and reducing the work function of the latter.
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Ryder, Matthew. « Physical phenomena in metal-organic frameworks : mechanical, vibrational, and dielectric response ». Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:c7a51278-19d7-45ae-825a-bac8040775a7.
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This thesis entails the utilisation of ab initio density functional theory (DFT) in conjunction with neutron and synchrotron spectroscopy to study the mechanical, vibrational, and dielectric response of metal-organic framework (MOF) materials at the molecular level. MOFs are crystalline materials with nanoscale porosity, which have garnered immense scientific and technological interest for a wide variety of innovative engineering applications. One part of the thesis involves using low-frequency lattice vibrations to characterise the various physical motions that are possible for framework materials. These collective modes detected at terahertz (THz) frequencies have been used to reveal a broad range of exciting possibilities. New evidence has been established to demonstrate that THz modes are intrinsically linked to anomalous elasticity underpinning gate-opening and pore-breathing mechanisms, and to shear-induced phase transitions and the onset of structural instability. The phenomenon of molecular rotor mechanisms and trampoline-like motions are also observed, along with the first experimental confirmation of coordinated shear dynamics. Additionally, a new method to characterise the effects of temperature, and hence thermally-induced structural amorphisation is reported. Finally, for the first time, the frequency-dependent (dynamic) dielectric response of MOF materials, across the extended infrared (IR) spectral region was reported. The results were obtained from experimental synchrotron radiation IR reflectivity and DFT to reveal the low-к dielectric response of MOFs and established structure-property trends that highlight them as promising systems for microelectronic device applications.
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Yadnum, Sudarat. « Tailoring complex heterogeneous metal-organic framework structures ». Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0299/document.
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Dans cette thèse, de nouvelles stratégies pour la préparation de matériaux de type Metal-Organic-Frameworks (MOF) ont été étudiés et développés. L’électrodeposition bipolaire indirecte (IBED) a été utilisé pour préparer ZIF-8 et HKUST-1 sur des substrats métalliques de façon simple et avec une sélectivité spatiale. Ce concept devrait pouvoir être généralisée pour la synthèse de nombreux autres composés MOF, permettant ainsi une synthèse pas chère et verte, conduisant à de nouvelles générations de composites de type Janus basés sur des MOFs. En outre, des électrodes avec une structure hiérarchique macro-/ microporeux de HKUST-1 ont été préparées par une technique de dissolution-dépôt électrochimique. L'approche de synthèse mis au point est très pratique en ce qui concerne la durée des expériences, et ouvre diverses applications pour les MOFs. Enfin des nanoparticules de métaux nobles sur un substrat à base de MIL-101 ont été préparées comme la dernière partie de l'étude expérimentale par dépôt colloïdal. Ce concept peut être généralisé pour la synthèse d'autres composites nanoparticules métalliques / MOF, et pourrait améliorer l'activité catalytique des MOFs. En dehors de l'étude expérimentale, afin de comprendre mieux la catalyse de matériaux MOF, le comportement catalytique de Cu (II) dans le MOF-505 a été théoriquement étudié pour la réaction d'aldolisation Mukayiama par la théorie de densité fonctionnelle et comparé à celui d'un autre catalyseur, Cu-ZSM-5. En outre, le comportement catalytique d'amas homo- et hétéro-bimétalliques, qui sont des complexes métalliques qui représentent les agrégats métalliques dans les MOFs, a également été étudié théoriquement pour la réaction de cycloaddition de dioxyde de carbone et des oxydes d'éthylèneIn this thesis, new strategies for the preparation of Metal 0rganic Frameworks (MOF) materials with designed structures were studied and developed. Indirect bipolar electrodeposition (IBED) was used to prepare ZIF-8 and HKUST-1 on metal substrates in a straightforward and site-selective way. This concept is expected to be able to be generalized for the synthesis of many other MOF compounds, thus allowing a cheap and green synthesis, leading to new generations of MOF-based Janus-type composites. Furthermore, rationally designed hierarchical macro-/microporous HKUST-1 electrodes were prepared via an electrochemical dissolution-deposition technique. The developed synthesis approach is very practical in terms of the time consumption, and opens up MOFs for various applications. Finally, MIL-101-supported noble metal nanoparticles were prepared as the last part of the experimental studies via a simple colloidal deposition technique. This concept might be generalized for the synthesis of other metal nanoparticle/MOF composites, and might improve the catalytic activity of MOFs. Apart from the experimental study, in order to gain a deeper insight into the catalysis of MOF materials, the catalytic behavior of Cu(II) in the paddle-wheel unit of MOF-505 was theoretically investigated for the Mukaiyama aldol reaction via the density functional theory and compared to that of another catalyst, Cu-ZSM-5 zeolite. Besides, the catalytic behavior of homo-metallic clusters and hetero-bimetallic clusters, that are the metal complexes representing the metal clusters in MOFs, were also theoretically investigated for the cycloaddition reaction of carbon dioxide and ethylene oxides
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Dawson, Daniel M. « Combined theoretical and experimental investigations of porous crystalline materials ». Thesis, University of St Andrews, 2014. http://hdl.handle.net/10023/7053.
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This thesis combines solid-state nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), chemical synthesis, isotopic enrichment and density-functional theory (DFT) calculations to provide insight into a number of microporous materials. The first class of materials studied is metal-organic frameworks (MOFs), where the presence of paramagnetic ions has a range of effects on the ¹³C NMR spectra, depending on the nature of the ligand-metal interactions. For the Cu²⁺-based MOFs, HKUST-1 and STAM-1, the assignment of the NMR spectra is non-intuitive, and unambiguous assignment requires specific ¹³C labelling of the organic linker species. It is shown that ¹³C NMR spectra of these two MOFs could act as a sensitive probe of the nature of “guest” molecules bound to the Cu²⁺. The second class of materials is aluminophosphates (AlPOs). It is shown that, using a series of relatively simple linear relationships with the crystal structure, the NMR parameters calculated by DFT (with calculation times of several hours) can be predicted, often with experimentally-useful accuracy, in a matter of seconds using the DIStortion analysis COde (DISCO), which is introduced here. The ambient hydration of the AlPO, JDF-2, to AlPO-53(A) is shown to occur slowly, with incomplete hydration after ~3 months. The resulting AlPO-53(A) is disordered and some possible models for this disorder are investigated by DFT. The final class of materials is gallophosphates (GaPOs), particularly GaPO-34 and related materials. The two as-prepared forms of GaPO-34 are characterised by solid-state NMR, and their calcination investigated by TGA and in-situ powder XRD. An unusual dehydrofluorinated intermediate phase is isolated and characterised for the first time by solid-state NMR. The fully calcined material is shown to be stable under anhydrous conditions, but hydrates rapidly in air. The hydrated material is stable under ambient conditions, but collapses upon heating. Partial dehydration without collapse is achieved by gentle heating or room-temperature evacuation. The impurity phases, GaPO₄ berlinite and GaPO-X are investigated by solid-state NMR and, while the structure of GaPO-X remains unknown, much structural information is obtained.
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Mohebbi, Elaheh. « Surface supported supramolecular architectures : an experimental and modeling study ». Doctoral thesis, Università degli studi di Padova, 2019. http://hdl.handle.net/11577/3427304.
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L’auto-organizzazione di molecole organiche su superfici solide è uno degli approcci più diffusi per la creazione di architetture supramolecolari supportate di dimensioni controllate e con proprietà innovative. L’uso combinato di differenti interazioni di natura non covalente adsorbato–adsorbato e adsorbato–substrato consente infatti la modulazione dell’associazione di specie distinte in modo quasi altrettanto accurato che nei sistemi biologici, fonte primaria di ispirazione per ciò che può essere realizzato artificialmente. Il consenso sull’uso d’interazioni intermolecolari estese non covalenti nell’ingegnerizzazione di nanostrutture bidimensionali supportate prive di difetti è unanime. Ciononostante, i materiali così ottenuti sono spesso fragili, incapaci di resistere a condizioni aggressive, privi di stabilità meccanica ed inefficienti nei processi di trasferimento di carica intermolecolare; sono cioè materiali inadatti per applicazioni tecnologiche. La produzione di sistemi nanostrutturati supportati con proprietà predeterminate, privi di difetti e con risvolti applicativi implica quindi la sintesi di network covalenti robusti, non caratterizzati dalle limitazioni di cui sopra. In questa tesi di dottorato si è voluta esplorare sia sperimentalmente sia teoricamente la possibilità di stabilizzare covalentemente network supramolecolari funzionali in una/due dimensioni stimolando la formazione di legami covalenti tra molecole preorganizzate su una superficie.The scientific community is nowadays focused on the design and the production of nm/μm-sized systems for their relevance to nanotechnology, energy production and storage, life science and environment. Advances in high performing computing and in synthetic/characterization methods make possible devising novel rational approaches to tailor properties of low-dimensional architectures of molecular networks on inorganic substrates; i.e., to control the electron transport properties of active layers and the reactivity of selected sites. As such, the self-assembly of functional architectures on appropriate surfaces is the most promising bottom-up approach to organize and integrate single molecules on solid substrates. As a consequence of the persistent progress in computational power and multiscale material modeling, new materials are less likely to be discovered by a trial-and-error approach. This points to a paradigm shift in modeling, away from reproducing known properties of known materials and towards simulating the properties of hypothetical composites as a forerunner to get real materials with desired characteristics. The interplay among multiscale material modeling, new synthetic routes and appropriate validation experiments is crucial to design the desired behavior at each length scale. In this PhD thesis we exploited integrated methodologies to provide interpretative tools about structure and functions of organic/inorganic hybrid nanostructured materials made of molecular mono-layers deposited on technological relevant substrates, suitable for applications in strategic areas such as catalysis, artificial photosynthesis, molecular electronics-magnetism and molecular recognition.
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Burrill, Daniel. « Density Functional Theory Study of Dilute Transition Metal Phthalocyanines ». ScholarWorks @ UVM, 2015. http://scholarworks.uvm.edu/graddis/508.
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Organometallic (OM) crystals are studied in fields ranging from spintronics to photovoltaics. This thesis focuses on studying a particular class of OM crystals known as transition metal-phthalocyanines (TM-Pc) - a molecular crystal composed of chains of planar OM molecules with a transition metal center and four coordinated pyrrole-aromatic rings joined by nitrogen atoms, similar to porphyrin. The structure resembles a dish rack pattern where the planar TM-Pcs of adjacent chains are oriented nearly perpendicular to each other. While TM-Pcs have been studied for decades due to their interesting optical properties and applications as dyes, there has been recent interest in understanding the magnetic properties with various transition metals.
Due to crystal arrangement, inter-chain interactions among TM-Pcs are relatively weak when compared to intra-chain interactions. This property allows the chains of TM-Pcs to be isolated and approximated as a pseudo 1D system. The electronic structure and spin exchange are computationally examined along chains of CuPc when they have been diluted with the metal-free variant, H2Pc. Density functional theory is employed with the Hubbard U correction to account for electron interactions on the copper d-orbitals. Since the diluted systems are effectively 1D with narrow bands along their stacking axis, a 1D Heisenberg model is applied where the exchange coefficient is determined through the Broken Symmetry method. Additionally, the effect of non-local corrections, used to determine structural features, on the Hubbard U and Heisenberg exchange coefficient, J, are discussed.
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McAllister, B. P. « A density functional theory study of reactions of metal and metal oxides ». Thesis, Queen's University Belfast, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426760.
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Burema, Shiri. « Inelastic Electron Tunneling Spectroscopy with the Scanning Tunneling Microscope : a combined theory-experiment approach ». Thesis, Lyon, École normale supérieure, 2013. http://www.theses.fr/2013ENSL0821.
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La Spectroscopie par Effet Tunnel Inélastique (IETS) avec un Microscope à Effet Tunnel (STM) est une nouvelle technique de spectroscopie vibrationnelle, qui permet de caractériser des propriétés très fines de molécules adsorbées sur des surfaces métalliques. Des règles de selection d’excitation vibrationnelle basées sur la symétrie ont été proposées, cependant, elles ne semblent pas exhaustives pour expliquer la totalité du mécanisme et des facteurs en jeu; elles ne sont pas directement transposables pour les propriétés d'un adsorbat et sont lourdes d'utilisation. Le but de cette thèse est donc d'améliorer ces règles de selection par une étude théorique. Un protocole de simulation de l'IETS a été développé, paramétré, et évalué, puis appliqué pour calculer des spectres IETS pour différentes petites molécules, qui sont systématiquement liées, sur une surface de cuivre. Des principes additifs de l'IETS ont été developpés, notamment concernant l’extension dans le vide de l’état de tunnel, l'activation/ quench sélectif de certains modes du aux propriétés électroniques de certains fragments moléculaires, et l'application de certaines règles d'addition de signaux IETS. De plus, des empreintes vibrationnelles par des signaux IETS ont été determinées pour permettre de différentier entre les orientations des adsorbats, la nature chimique des atomes et les isomères de structures. Une stratégie simple utilisant les propriétés de distribution de la densité électronique de la molécule isolée pour prédire les activités IETS sans des couts importants de calculs a aussi été développée. Cette expertise a été utilisée pour rationaliser et interpréter les mesures expérimentales des spectres IETS pour des métalloporphyrines et métallophtalocyanines adsorbées. Ces études sont les premières études IETS pour des molécules aussi larges et complexes. L'approche expérimentale a permis de déterminer les limitations actuelles des simulations IETS. Les défauts associés à l'identification ont été résolus en faisant des simulations d'images STM complémentairesInelastic Electron Tunneling Spectroscopy (IETS) with the Scanning Tunneling Microscope (STM) is a novel vibrational spectroscopy technique that permits to characterize very subtle properties of molecules adsorbed on metallic surfaces. Its proposed symmetry-based propensity selection rules, however, fail to fully capture its exact mechanism and influencing factors; are not directly retraceable to an adsorbate property and are cumbersome. In this thesis, a theoretical approach was taken to improve them. An IETS simulation protocol has been developed, parameterized and benchmarked, and consequently used to calculate IETS spectra for a set of systematically related small molecules on copper surfaces. Extending IETS principles were deduced that refer to the tunneling state’s vacuum extension, the selective activating/quenching of certain types of modes due to the moieties’ electronic properties, and the applicability of a sum rule of IETS signals. Also, fingerprinting IETS-signals that enable discrimination between adsorbate orientations, the chemical nature of atoms and structural isomers were determined and a strategy using straightforward electronic density distribution properties of the isolated molecule to predict IETS activity without (large) computational cost was developed. This expertise was used to rationalize and interpret experimentally measured IETS spectra for adsorbed metalloporphyrins and metallophthalocyanines, being the first IETS studies of this large size. This experimental approach permitted to determine the current limitations of IETS-simulations. The associated identification shortcomings were resolved by conducting complementary STM-image simulations
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Dang, Li. « Density functional theory studies of copper(I) mediated borylation and carboxylation reactions / ». View abstract or full-text, 2010. http://library.ust.hk/cgi/db/thesis.pl?CHEM%202010%20DANG.
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Schiros, Theanne. « Water-Metal Surfaces : Insights from core-level spectroscopy and density functional theory ». Doctoral thesis, Stockholm University, Department of Physics, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-7435.
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Computational methods are combined with synchrotron-based techniques to analyze the structure and bonding of water and water plus hydroxyl at metal surfaces under UHV and at near-ambient conditions. Water-metal interaction plays a crucial role in a multitude of cosmic, atmospheric and biological phenomena as well as heterogeneous catalysis, electrochemistry and corrosion. A spotlight of renewed interest has recently been cast on water-metal systems due to their relevance for surface chemical reactions related to the production and utilization of hydrogen as a clean energy carrier. In particular, H2O and OH are essential reaction intermediates in the renewable production of hydrogen from sunlight and water and in fuel cell electrocatalysis.
Fuel cells are considered one of the most promising power generation technologies for a sustainable energy future. A mechanistic understanding of the oxygen reduction reaction (ORR) pathway, including the role of electronic and geometric structure of the catalyst, is essential to the design of more efficient fuel cell catalysts. This is intimately connected to fundamental factors that affect the ability to form water-metal bonds as well as the site occupation and orientation of the adsorbed H2O and OH at active metal surfaces.
Key relationships related to critical issues in the fuel cell reaction are illuminated by the synergy of theory and experiment in this thesis. We emerge with a detailed understanding of the structure of the water-metal interface and the factors that rule the wettability of a metal surface, including geometric and electronic structure effects and the influence of coadsorbed species. We show that the preferred microscopic orientation of the water monolayer has consequences for macroscopic properties, and reveal the origin of the hydrophobic water layer. Finally, we identify a cooperativity effect that drives the stability of the mixed water/hydroxyl layer at metal surfaces, an important ORR intermediate.
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Olaoye, Olufemi Opeyemi. « Density functional calculation of simple molecules ». Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/20345.
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Thesis (MSc)--Stellenbosch University, 2012.AFRIKAANSE OPSOMMING: Berekeninge met Density Functional Theory (DFT) is ’n nuttige tegniek om die dinamika van molekules op potensiële energievlakke te verstaan. Beginnende met ’n prototipe molekuul formaldimien, wat die kern vorm van die groter fotochromiese molekuul dithizonatophenyl kwik (DPM), word die modellering van die molekuul meer ingewikkeld tot laasgenoemde bestudeer kan word asook sy fotochromiese afgeleides wat vervanging van elektronryk en elektronarm radikale by orto, meta en para posisies van die phenyl ringe insluit. DFT berekeninge word met spektra van Absorpsiespektroskopie met UV en sigbare lig asook tyd opgeloste spektra, verkry dmv femtosekondespektroskopie, vergelyk. In pol^ere aprotiese, pol^ere protiese en nie-pol^ere oplosmiddels, isomeriseer die molekuul om die C=N dubbelbinding. Daar kan tussen die twee isomere onderskei word deur dat die een in oplossing in sy grondtoestand blou en die ander een oranje voorkom. Die isomerisering is’n fotogeinduseerde proses. Die optimering van die molekul^ere struktuur, absorpsiespektra, oplosmiddel-afhanklikheid, en potensiële energievlak metings van die molekuul word bestudeer. Die sterk/swak wisselwerking wat in pol^ere protiese/aprotiese oplosmiddels verskyn word geopenbaar deur die hoe/lae absorpsie van die sekond^ere bande van die molekules. Daar is gevind dat die absorpsiespektra van DPM bathochromies in oplosmiddels met hoë diëlektriese konstantes is. Vir die potensiële energievlak berekeninge van die grondtoestand word rigiede en ontspanne metodes gebruik waar laasgenoemde met gebroke simmetrie berekeninge verkry word. Van alle metodes wat vir berekeninge gebruik was, gee die B3LYP/CEP-31G metode die beste benadering aan eksperimentele data. Alle berekeninge word gedoen met twee bekende sagteware pakkette; Amsterdam Density Functional (ADF) en Gaussian, wat op twee verskillende DFT metodes gebaseer is.
ENGLISH ABSTRACT: Density functional theory is a useful computational tool in the understanding of molecular dynamics on potential energy surfaces. Starting with a prototype molecule formaldimine, the photochromic molecule dithizonatophenylmercury II (DPM) and a set of its photochromic derivatives, (involving substitutions of electron donating and electron withdrawing substituents at ortho, meta and para positions of the dithizonato phenyl rings), are studied through density functional calculation in comparison with steady state absorption spectra obtained from UV-Visible and femto second spectroscopy experiments. In polar aprotic, polar protic and non-polar solvents these molecules isomerise around C=N double bond chromophore, from orange electronic ground states to blue electronic ground states upon photo-excitation. We investigate the structural optimisations, the absorption spectra, the solvent dependence and the potential energy surface (PES) of these molecules. The strong (weak) interactions exhibited by the polar protic (aprotic) solvents used are revealed through high (low) absorbance in the secondary bands of these molecules. The absorption spectra of DPM are found to be bathochromic in solvents with high dielectric constants. For the ground state PES calculation we make use of rigid and relaxed methods, and the latter is obtained through broken symmetry calculation. Of all the methods used in calculation, B3LYP/CEP-31G method gives the best approximation to the experimental data. All calculations are done using the two renown software, Amsterdam Density Functional (ADF) and Gaussian, availing their different density functional methods.
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Tang, Miru. « DENSITY FUNCTIONAL THEORY STUDIES ON THE STRUCTURE AND CATALYTIC ACTIVITY OF METAL OXIDES ». OpenSIUC, 2018. https://opensiuc.lib.siu.edu/dissertations/1602.
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In this dissertation, I present four projects on the fundamental study of the surface configurations and reactivity of the metal oxides using density functional theory computational method. In the first project, we studied the formaldehyde adsorption and diffusion on rutile TiO2 (110) surface. By comparing the adsorption of formaldehyde on stoichiometric and defective TiO2 surfaces under the same condition, we evaluated the effect of surface oxygen vacancy on their interaction with formaldehyde. The project involved close collaboration with Dr. Zhenrong Zhang’s group of Baylor University who studied the formaldehyde chemistry on rutile TiO2(110) surface using a combination of STM and other surface science techniques. In the second project, we compared the surface chemistries of formaldehyde and formic acid on rutile TiO2 and SnO2, two structurally similar but chemically different oxides. We analyzed the oxidation of formaldehyde to formic acid on two oxides and assessed the role of surface oxygen in the oxidation. In the third project, we studied the oxygen evolution reaction (OER) catalyzed by γ-FeOOH (010) under the alkaline condition. The OER process was divided into four elementary steps and the potential energy profiles of these steps on three terminations of the γ-FeOOH (010) surface were mapped out. Based on the computed reaction energies, we determined the most probable OER reaction pathway on each surface termination. We found that partially exposed surface Fe sites were the active sites for the OER process. In the fourth project, we studied the potential of iron oxides (FeOx) and iron-titanium mixed oxides (FeTiOx) as solid oxygen carriers for the chemical looping combustion (CLC) process. As oxygen carriers for CLC, FeOx and FeTiOx in fully oxidized forms went through a series of reduction steps by reacting with the fuel molecules. The reduced oxides were then re-oxidized in an air reactor to restore their oxygen. By studying the surface oxygen vacancy formation and oxygen diffusion, we gained insights into the initial stage of reduction process and activities of FeOx and FeTiOx as well as the effect of Ti on oxygen carrying properties of FeTiOx for CLC.
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Tafur, Sergio. « NONLINEAR OPTICAL PROPERTIES OF ORGANIC CHROMOPHORES CALCULATED WITHIN TIME DEPENDENT DENSITY FUNCTIONAL THEORY ». Master's thesis, University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4079.
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Time Dependent Density Functional Theory offers a good accuracy/computational cost ratio among different methods used to predict the electronic structure for molecules of practical interest. The Coupled Electronic Oscillator (CEO) formalism was recently shown to accurately predict Nonlinear Optical (NLO) properties of organic chromophores when combined with Time Dependent Density Functional Theory. Unfortunately, CEO does not lend itself easily to interpretation of the structure activity relationships of chromophores. On the other hand, the Sum Over States formalism in combination with semiempirical wavefunction methods has been used in the past for the design of simplified essential states models. These models can be applied to optimization of NLO properties of interest for applications. Unfortunately, TD-DFT can not be combined directly with SOS because state-to-state transition dipoles are not defined in the linear response TD approach. In this work, a second order CEO approach to TD-DFT is simplified so that properties of double excited states and state-to-state transition dipoles may be expressed through the combination of linear response properties. This approach is termed the a posteriori Tamm-Dancoff approximation (ATDA), and validated against high-level wavefunction theory methods. Sum over States (SOS) and related Two-Photon Transition Matrix formalism are then used to predict Two-Photon Absorption (2PA) profiles and anisotropy, as well as Second Harmonic Generation (SHG) properties. Numerical results for several conjugated molecules are in excellent agreement with CEO and finite field calculations, and reproduce experimental measurements well.M.S.
Department of Physics
Sciences
Physics MS
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Paget, Veronica J. « The modelling of transition metal centres using molecular mechanics and density functional theory ». Thesis, University of Bath, 1996. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320428.
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Lynch, Mark Francis. « Chemical reactions of small molecules on metal surfaces : a density functional theory study ». Thesis, Queen's University Belfast, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314017.
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Elliott, J. D. « The application of linear-scaling Density Functional Theory to large metal oxide nanotubes ». Thesis, University of Liverpool, 2016. http://livrepository.liverpool.ac.uk/3003340/.
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Durivage, Jason Curtis. « Ligand Effects on Metal-Metal Bonding : Photoelectron Spectroscopy and Electronic Structure Calculations of Dimetal Paddlewheel Complexes ». Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/145427.
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Paddlewheel complexes are molecules in which two interacting metal atoms are bridged by four chelating ligands. This class of complexes has a large range of electronic variability while keeping a rigid geometric structure. This variability has led to their use as catalysts, strong reductants, anti-tumor agents, and electron transfer agents. This dissertation examines the effects of changing both the dimetal core and the surrounding ligands on the electronic structure properties of the paddlewheel complexes. Examination of Bi₂(O₂CCF₃)₄, a p-orbital dimetal paddlewheel complex, provided a way to probe the orbitals that are important in metal-ligand σ bonding. The b(1g) and b(2u) ligand orbitals of Bi₂(O₂CCF₃)₄ have no dimetal orbital counterpart, unlike the case of the more familiar d-orbital dimetal paddlewheel complexes such as Mo₂(O₂CCF₃)₄. This had the effect of destabilizing these ligand orbitals compared to d-orbital paddlewheel complexes. The ligand a1g orbital in Bi₂(O₂CCF₃)₄ was also destabilized due to nodal differences in the dimetal σ orbital. The unusual coincidence of Mo-Mo σ and π ionization bands is due to a greater amount of ligand character in the Mo-Mo σ orbital compared to its ditungsten analogue, which has separate ionization bands for the σ and π bonds. A series of p-substituted dimolybdenum tetrabenzoate complexes was synthesized and studied by photoelectron spectroscopy in order to further examine the delocalization of electron density from the metals to the ligands in these complexes. A 0.89 eV shift in the δ ionization band was observed from Mo₂(O₂CPh-p-OMe) ₄ and Mo₂(O₂CPh-p-CF₃)₄. Overlap effects are the major factor causing the shift in the δ bond ionization, as the calculated charges on the molybdenum and oxygen atoms did not vary significantly on change of substituent. Molybdenum and tungsten guanidinate paddlewheel complexes have promise as good reducing agents due to their extremely low ionization energies. The solubility of the complexes poses a problem for their widespread adoption for use as reducing agents. Alkyl substituents were added to the complexes to increase their solubility. W₂(TEhpp)₄ was observed to have the lowest ionization energy at 3.71 eV (vertical ionization) and 3.40 eV (onset ionization) of any molecule yet prepared.
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Lin, Xi 1973. « First-principles density functional theory study of sulfur oxide chemistry on transition metal surfaces ». Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/29642.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2003.Vita.
Includes bibliographical references (p. 297-309).
In this thesis, the chemistry of sulfur oxides on transition metals is studied extensively via first-principles density functional theory (DFT) computations, focusing on the chemical reactivity and selectivity in sulfur poisoning chemical processes that address environmental concerns. The systematic approach we establish can be extended to general computational studies of small gas-phase molecules interacting with extended surfaces or finite-size clusters. The thesis starts with a theoretical presentation of modem quantum many-body theory that brings together mean-field theory, DFT, and Green's function quantum Monte Carlo theory. The essence of chemical reactivity theory in the framework of DFT is emphasized. The thesis continues with an extensive survey of the current status of sulfur oxide chemistry and an overall presentation of our computational approaches towards a detailed understanding of chemical reactivity and selectivity. The basic guidelines in chemical reactivity are systematically constructed by computed comprehensive thermodynamic data of surface S, O, SO, SO2, SO3, and S04 species as a function of coverage at low and intermediate temperatures. Under these basic guidelines, experimentally measured surface spectra are interpreted, contradictory experimental observations are resolved, and applicable experimental measurements are suggested for confirming computational predictions. Moreover, the chemical reactivity study is supplemented by our chemical kinetics study focusing on the catalytic oxidation of SO2 under oxygen rich conditions. This is the key process that hampers the implementation of the next-generation automotive catalytic converter. The revealed Langmuir-Hinshelwood mechanism demonstrates the essential catalytic performance of the Pt(1 11) surface.
(cont.) The thesis closes with a chemical selectivity analysis of the effects of catalyst particle size on chemisorption of gas-phase adatoms. In summary, the presentation of the chemistry of sulfur-containing molecules in this work is aimed at a scientific understanding of the strong poisoning effects in heterogeneous catalysis. However, the chemistry of sulfur-containing molecules has many more fundamental implications, such as in designing novel re-conjugated conducting devices for quantum computers. The underlying hybrid bonding flexibility of sulfur allows it to simultaneously bind to heavy transition metal atoms (such as Pt, Cu, or Au) and first-row atoms (such as oxygen atoms or carbon atoms in organic molecules).
by Xi Lin.
Ph.D.
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Wood, Christopher Alan. « Theoretical investigation of polar zinc oxide surface modification via phosphonic acid self-assembled monolayers ». Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/43584.
Texte intégralRésumé :
The interface of a zinc-terminated polar zinc oxide surface (0002) with a series of chemisorbed fluorinated benzylphosphonic acids has been studied using density functional theory. The calculations indicate that there is a substantial change in the binding energies and work function modification depending on the binding motif. The results also indicate that there is a pronounced difference in the magnitude and trends of the factors determining the total change in work function. The oxygen core-level binding shifts have been calculated and compared to available experimental data.
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Bjärnhall, Prytz Nicklas. « Interactions of cellulose and aromatic organic molecules modelled with density functional theory : A computational study ». Thesis, Uppsala universitet, Nanoteknologi och funktionella material, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-254596.
Texte intégralRésumé :
In this study, the interaction energies between aromatic organic molecules (AOMs) and cellulose are explored using density functional theory (DFT) through the software SIESTA and the exchange-correlational functional VDW-DRSLL. Three AOMs will be modelled: benzene, benzamide and benzoic acid. Firstly, the interaction energies of the dimers of the AOMs are determined. Then, the obtained interaction energies of the cellulose-AOM complexes are compared to the former in order to decide which interaction is stronger. It is found that the studied AOMs are more likely to interact with cellulose than with another identical monomer; benzamide has the highest propensity to interact, followed by benzoic acid and benzene. Furthermore, for all interaction energy calculations a counterpoise correction term will be introduced as an addition to the SIESTA optimisation and it will be shown that without this correction the acquired energy minima will deviate significantly from accepted values from previous studies.
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Li, Qiang. « Density functional theory studies of biomass conversion on metal surfaces : from small to large molecules ». Doctoral thesis, Universitat Rovira i Virgili, 2017. http://hdl.handle.net/10803/461081.
Texte intégralRésumé :
En aquesta tesi s'han proposat i calculat una sèrie de mecanismes de reacció relacionats amb diverses molècules derivades de biomassa sobre models de superficie utilitzant el paquet VASP (Vienna Ab initio simulation package).
S'ha realitzat una investigació multiescala sobre formació d'hidrogen a partir de petites molècules de metanol, etanol, etilenglicol i glicerol. Els càlculs dels alcohols C1 i C2 es realitzaren en superfícies de Cu(111) i Ru(0001), mentre que els de glicerol només sobre Ru(0001). Es van optimitzar les geometries d'enllaç dels intermedis complets, així com s'ha proposat la descomposició detallada i els mecanismes d'hidrogenació relacionats amb dites espècies. S'han analitzat les relacions BEP i TSS i s'ha realitzat també una simulació microcinètica ab initio sota diferents condicions.
Hidrogenació d'àcid levulínic a gamma-valerolactona sobre Ru(0001) i sobre Ru(0001) decorada amb HHDMA. S'ha proposat el mecanisme de formació de l'anell intramolecular sobre la superfície de Ru(0001). S'ha elucidat l'acidesa interfacial i les estructures locals a la interfície HHDMA-Ru(0001) que promouen la velocitat de catàlisi i l'estabilitat front l'oxidació.
Hidrogenació de glucosa i manosa als seus alcohols de sucre a la superfície Ru(0001). Les reaccions dels isòmers lineals i cíclics han estat calculades i comparades entre dues molècules de sucre i amb els resultats experimentals. L'autor va trobar que concentracions de diferents isòmers reactius en la fase líquida, diferents energies d'adsorció i mecanismes de reacció treballen conjuntament per controlar les velocitats de reacció totals.
Descomposició i hidrogenació de lignina a les superfícies Ni(111) i Ni(111)dopades amb Ru. S'han aclarit els mecanismes de descomposició de lignina basats en un model de dimer més complicat. S'han discutit els efectes de l'estereocentre en les seves conversions i també s’han dilucidat els efectes de dopatge de Ru promocionant el comportament dels catalitzadors.En esta tesis se han propuesto y calculado una serie de mecanismos de reacción relacionados con diversas moléculas derivadas de biomasa sobre modelos de superficie usando el paquete VASP (Vienna Ab initio simulation package). Se ha realizado una investigación multiescala sobre formación de hidrógeno a partir de moléculas pequeñas de metanol, etanol, etilenglicol y glicerol. Los cálculos de los alcoholes C1 y C2 se realizaron en superficies de Cu(111) y Ru(0001), mientras que los de glicerol sólo en Ru(0001). Se optimizaron las geometrías de enlace de los intermedios completos, así como se ha propuesto la descomposición detallada y los mecanismos de hidrogenación relacionados con dichas especies. Se han analizado las relaciones BEP y TSS y se ha realizado también una simulación microcinética ab initio en diferentes condiciones. Hidrogenación de ácido levulínico a gamma-valerolactona sobre Ru(0001) y sobre Ru(0001) decorada con HHDMA. Se ha propuesto el mecanismo de formación del anillo intramolecular en la superficie de Ru(0001). Se ha elucidado la acidez interfacial y las estructuras locales en la interfaz HHDMA-Ru(0001) que promueven la velocidad de catálisis y la estabilidad frente a la oxidación. Hidrogenación de glucosa y manosa a sus alcoholes de azúcar sobre la superficie de Ru(0001). Las reacciones de los isómeros lineales y cíclicos se han calculado y comparado entre dos moléculas de azúcar y con los resultados experimentales. El autor encontró que concentraciones de diferentes isómeros reactivos en la fase líquida, diferentes energías de adsorción y mecanismos de reacción trabajan juntos para controlar las velocidades de reacción totales. Descomposición de lignina e hidrogenación sobre superficies de Ni(111) y Ni(111) dopadas con Ru. Se han esclarecido los mecanismos de descomposición de la lignina basados en un modelo de dímero más complicado. Los efectos del estereocentro en sus conversiones se han discutido y los efectos de dopaje de Ru promocionando el comportamiento de los catalizadores también se ha aclarado.
In this thesis, a series of surface reaction mechanisms related with various biomass derived molecules on slab models have been proposed and computed by using the Vienna Ab initio simulation package (VASP). 1 Multiscale investigation of hydrogen releasing from small molecules of methanol, ethanol, ethylene glycol, and glycerol have been studied. C1 and C2 alcohols’ calculations are performed both on Cu(111) and Ru(0001) surfaces and glycerol is on Ru(0001). Complete intermediates binding geometries were optimized, detailed decomposition, hydrogenation mechanisms related with these species have been proposed. BEP and TSS relationship have been analyzed and ab initio microkinetic simulation under different conditions has been also performed. 2 Glucose and mannose hydrogenation to their sugar alcohols on Ru(0001) surface. Reactions from linear and ring isomers have been calculated and compared between two sugar molecules, and compared with experiment results. The author found that concentrations of different reactant isomers in the liquid phase, different adsorption energies and reaction mechanisms work together to control the overall reaction rates. 3 Levulinic acid hydrogenation to gamma-valerolactone on Ru(0001) and HHDMA decorated Ru(0001) surface. Intramolecular ring formation mechanism on Ru(0001) surface has been outlined. Interfacial acidity and local structures in the HHDMA-Ru(0001) interface which promote the catalysis rate and stability against oxidation have been illuminated. 4 Lignin decomposition and hydrogenation on Ni(111) and Ru doped Ni(111) surfaces. Lignin decomposition mechanisms based on more complicated dimer model have been clarified. Stereocenter effects in its conversions have been discussed and the Ru doping effects on promoting the catalysts behavior is also elucidated.
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Sheen, Paul David. « Towards a hybrid density functional theory and molecular mechanics model for large transition metal systems ». Thesis, University of Bath, 1995. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296297.
Texte intégral
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Durr, Christopher Blair. « The Effect of Metal Containing Ligands on The Metal-Metal Quadruple Bond : Structure, Synthesis, And Photophysics ». The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1429542171.
Texte intégral
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Thulasi, Sunita. « Theory of the two-dimensional airy electron gas Hartee-Fock and density-functional studies / ». Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4111.
Texte intégralRésumé :
Thesis (Ph. D.)--University of Missouri-Columbia, 2006.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (May 17, 2007) Vita. n following parenthesis in formula (LaTiO₃) should be subscript. Includes bibliographical references.
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Clayborne, Penee. « Density Functional Studies of the Stability of Clusters ». VCU Scholars Compass, 2010. http://scholarscompass.vcu.edu/etd/2194.
Texte intégralRésumé :
Theoretical studies using the Kohn-Sham density functional formalism have been carried out to identify and investigate the stability of a variety of atomic clusters for their use in cluster assembled materials. The stable behavior found in a cluster system provides a way to classify inorganic clusters. The clusters in this study can be categorized in one of the following, jellium, all-metal aromatic, Zintl analogue or as a covalent metal-carbide. By understanding the electronic structure and ultimately the stable nature of a cluster first, it is proposed one can construct assemblies based on the stable cluster. The methodology presented is a viable way to design future nanomaterials with a variety of architectures and precise control over properties based on stable cluster motifs.
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Brett, Constance M. « Investigation of the structure and bonding of metal complexes through the use of density functional theory ». Connect to this title online, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1118688725.
Texte intégralRésumé :
Thesis (Ph. D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xxxi, 309 p.; also includes graphics Includes bibliographical references. Available online via OhioLINK's ETD Center
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Galstyan, Artur [Verfasser]. « Accurate redox potentials of transition metal complexes calculated using density functional theory and electrostatics / Artur Galstyan ». Berlin : Freie Universität Berlin, 2008. http://d-nb.info/1023261499/34.
Texte intégral
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Le, Jiabo. « Simulating electric double layers at transition metal-water interfaces from density functional theory based molecular dynamics ». Thesis, University of Aberdeen, 2017. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=235395.
Texte intégralRésumé :
This PhD project aims at understanding the electric double layers (EDLs) at transition metal-water interfaces with density functional theory based molecular dynamics (DFTMD). We plan to develop a method for computationally determining the electrode potential of an interface, which bridges experiments and theoretical computation. After that, we will investigate the microscopic structure of the EDLs, including ion distribution, water orientation, hydrogen bonding and so on. Furthermore, we are interested in the charge transfer between metal surface and water at different configurations, and some consequences this may lead to. In the first part, we have simulated Pt(111)-, Au(111)-, Pd(111)- and Ag(111)-water interfaces at a well-defined condition, potential of zero charge (PZC), by DFTMD. We find the water coverage of the metal surface is ⇠0.8ML, and there is no ordered pattern formed at room temperature. Moreover, we have characterised three configurations (watA, watB-down and watB-up) from the surface water layer, and revealed their hydrogen bonding networks. In the second part, we have developed a computationally efficient scheme for determining the electrode potential of the metal-water interfaces with respect to standard hydrogen electrode (SHE), and obtained the PZC values of Pt(111), Au(111), Pd(111) and Ag(111)-water interfaces within a good accuracy. Furthermore, we find that the interface dipole potentials are almost entirely caused by charge transfer from water and to the metal surfaces, the magnitude of which depends on the bonding strength between water and the metals, while water orientation hardly contributes at the PZC condition. In the third part, we have calculated the vibrational spectrum of the chemisorbed water on Pt(111) and Au(111), and found their peak positions of the stretch vibrational frequency are red-shifted, the magnitude of which is dependent to the strength of the metal-water interaction and the local hydrogen bonding. We have also suggested that the chemisorbed water is the source of the peaks at 2850-3000 cm-1 observed in experiments. In the last part, we have simulated a series of EDLs at Au(111)-water interfaces, their reliability is confirmed by comparing the differential capacitance with experimental values. We find the Stern layer gets compressed and the partial solvation layer of the ion is peeled off at a negatively charged surface. Moreover, we find the configuration of the interfacial water is reoriented from 'parallel water', to 'H-downwater', then further to 'perpendicular water' when the metal surface is progressively charged with electrons.
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Posysaev, S. (Sergei). « Applications of density functional theory for modeling metal-semiconductor contacts, reaction pathways, and calculating oxidation states ». Doctoral thesis, Oulun yliopisto, 2018. http://urn.fi/urn:isbn:9789526221328.
Texte intégralRésumé :
Abstract Density functional theory (DFT) is a well-established tool for calculating the properties of materials. The volume of DFT-related publications doubles every 5–6 years, which has resulted in the appearance of continuously growing open material databases, containing information on millions of compounds. Furthermore, the results of DFT computations are frequently coupled with experimental ones to strengthen the computational findings. In this thesis, several applications of DFT related to physics and chemistry are discussed. The conductivity between MoS₂ and transition metal nanoparticles is evaluated by calculating the electronic structure of two different models for the nanoparticles. Chemical bonding of Ni to the MoS₂ host is proven by the system’s band alignment. To meet the demand for cleaner fuel, the applicability of the (103) edge surface of molybdenum disulfide in relation to the early stages of the hydrodesulfurization (HDS) reaction is considered. The occurrence of the (103) edge surface of molybdenum disulfide in the XRD patterns is explained. A method for calculating oxidation states based on partial charges using open materials databases is suggested. We estimate the applicability of the method in the case of mixed valence compounds and surfaces, showing that DFT calculations can be used for the estimation of oxidation statesTiivistelmä Tiheysfunktionaaliteoria (density functional theory, DFT) on yleisesti käytetty työkalu laskennallisessa materiaalitutkimuksessa. DFT:llä tuotettujen julkaisujen määrä kaksinkertaistuu 5–6 vuoden välein, minkä johdosta käytettävissä on jatkuvasti kasvava määrä avoimia materiaalitietokantoja, joihin on talletettu miljoonien yhdisteiden ominaisuuksia. DFT-laskujen tuloksia täydennetään myös usein kokeellisilla tuloksilla. Tässä työssä tarkastellaan tiheysfunktionaaliteorian sovelluksia fysiikassa ja kemiassa. MoS₂:n ja metallisten nanopartikkelien välistä johtavuutta on tutkittu mallintamalla erilaisia nanopartikkeleita. Nikkelin ja MoS₂:n välinen kemiallinen sidos selittyy systeemin energiavöiden kohdistumisella. MoS₂:n (103)-pinnan soveltuvuutta rikinpoistoreaktion varhaisissa vaiheissa on tutkittu tarkoituksena löytää uusia menetelmiä puhtaan polttoaineen tuottamiseksi. Myös (103)-pinnan esiintyminen röntgendiffraktiokuvissa selitetään. Työssä on myös esitetty menetelmä hapetustilojen laskemiseksi tietokannoista löytyvien laskettujen varausjakaumien avulla. Menetelmän soveltuvuutta on tarkasteltu erilaisille yhdisteille ja pinnoille. Tämä tarkastelu osoittaa, että DFT-tuloksia voidaan käyttää hapetustilojen laskemiseen
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Bhandari, Srijana. « AN ELECTRONIC STRUCTURE APPROACH TO UNDERSTAND CHARGE TRANSFERAND TRANSPORT IN ORGANIC SEMICONDUCTING MATERIALS ». Kent State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=kent1606836665551399.
Texte intégral
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Ullah, Habib. « First-principles density functional theory study of novel materials for solar energy conversion and environment applications ». Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/32949.
Texte intégralRésumé :
To design an efficient solar energy conversion device, theoretical input is extremely important to provide the basic guideline for experimental scientists, to fabricate the most efficient, cheap, and stable device with less efforts. This desire can be made possible if computational scientist use a proper theoretical protocol, design an energy material, then the experimentalist will only invest weeks or months on the synthetic effort. This thesis highlights my recent efforts in this direction. Monoclinic BiVO4 is has been using as a photocatalyst due to its stability, cheap, easily synthesizable, narrow band gap and ideal VB (-6.80 eV vs vacuum) but inappropriate CB (-4.56 eV vs vacuum) edge position, responsible for its low efficiency. We have carried out a comprehensive experimental and periodic density functional theory (DFT) simulations of the pristine, Oxygen defective (Ov), Se doped monoclinic BiVO4 and heterojunction with Selenium (Se-BiVO4), to improve not only its CB edge position but photocatalytic and charge carrier properties. It is found that Ov (1% Oxygen vacancy) and mild doped BiVO4 (1 to 2% Se) are thermodynamically stable, have ideal band edges ~ -4.30 eV), band gaps (~1.96 eV), and small effective masses of electrons and holes. We have also investigated the contribution of Se to higher performance by effecting morphology, light absorption and charge transfer properties in heterojunction. Finally, it is found that Se makes a direct Z-scheme (band alignments) with BiVO4 where the photoexcited electron of BiVO4 recombine with the VB of Se, consequences electron-hole separation at Se and BiVO4, respectively, as a result, enhanced photocurrent is obtained. Theoretical study of β-TaON in the form of primitive unit cell, supercell and its N, Ta, and O terminated surfaces are carried out with the help of periodic DFT. Optical and electronic properties of all these different species are simulated, which predict TaON as the best candidate for photocatalytic water splitting contrast to their Ta2O5 and Ta3N5 counterparts. The calculated bandgap, valence band, and conduction band edge positions predict that β-TaON should be an efficient photoanodic material. The valence band is made up of N 2p orbitals with a minor contribution from O 2p, while the conduction band is made up of Ta 5d. Turning to thin films, the valence band maximum; VBM (−6.4 eV vs. vacuum) and the conduction band minimum; CBM (−3.3 eV vs. vacuum) of (010)-O terminated surface are respectively well below and above the redox potentials of water as required for photocatalysis. Charge carriers have smaller effective masses than in the (001)-N terminated film (VBM −5.8 and CBM −3.7 eV vs. vacuum). However, due to wide band gap (3.0 eV) of (010)-O terminated surface, it cannot absorb visible wavelengths. On the other hand, the (001)-N terminated TaON thin film has a smaller band gap in the visible region (2.1 eV) but the bands are not aligned to the redox potential of water. Possibly a mixed phase material would produce an efficient photoanode for solar water splitting, where one phase performs the oxidation and the other reduction. Computational study of an optically transparent, near-infrared-absorbing low energy gap conjugated polymer, donor−acceptor−donor (D-A-D) with promising attributes for photovoltaic application is reported herein. The D and A moiety on the polymeric backbone have been found to be responsible for tuning the band gap, optical gap, open circuit (Voc) and short-circuit current density (Jsc) in the polymers solar cells (PSC). Reduction in the band gap, high charge transformation, and enhanced visible light absorption in the D-A-D system is because of strong overlapping of molecular orbitals of D and A. In addition, the enhanced planarity and weak steric hindrance between adjacent units of D-A-D, resulted in red-shifting of its onset of absorption. Finally, PSC properties of the designed D-A-D was modeled in the bulk heterojunction solar cell, which gives theoretical Voc of about 1.02 eV. DFT study has been carried out to design a new All-Solid-State dye-sensitized solar cell (SDSC), by applying a donor-acceptor conjugated polymer instead of liquid electrolyte. The typical redox mediator (I1−/I3−) is replaced with a narrow band gap, hole transporting material (HTM). A unique “upstairs” like band energy diagram is created by packing N3 between HTM and TiO2. Our theoretical simulations prove that the proposed configuration will be highly efficient as the HOMO level of HTM is 1.19 eV above the HOMO of sanitizer (dye); providing an efficient pathway for charge transfer. High short-circuit current density and power conversion efficiency is promised from the strong overlapping of molecular orbitals of HTM and sensitizer. A low reorganization energy of 0.21 eV and exciton binding energy of 0.55 eV, confirm the high efficiency of HTM. Theoretical and experimental studies of a series of four porphyrin-furan dyads were designed and synthesized, having anchoring groups, either at meso-phenyl or pyrrole-β position of a zinc porphyrin based on donor–π–acceptor (D–π–A) approach. The porphyrin macrocycle acts as donor, furan hetero cycle acts as π-spacer and either cyanoacetic acid or malonic acid group acts as acceptor. Optical bandgap, natural bonding, and molecular bonding orbital (HOMO–LUMO) analysis confirm the high efficiency pyrrole-β substituted zinc porphyrins contrast to meso-phenyl dyads. DFT study of polypyrrole-TiO2 composites has been carried out to explore their optical, electronic and charge transfer properties for the development of an efficient photocatalyst. Titanium dioxide (Ti16O32) was interacted with a range of pyrrole (Py) oligomers to predict the optimum composition of nPy-TiO2 composite with suitable band structure for efficient photocatalytic properties. The study has revealed that Py-Ti16O32 composites have narrow band gap and better visible light absorption capability compared to individual constituents. A red-shifting in λmax, narrowing band gap, and strong intermolecular interaction energy (-41 to −72 kcal/mol) of nPy-Ti16O32 composites confirm the existence of strong covalent type interactions. Electron−hole transferring phenomena are simulated with natural bonding orbital analysis where Py oligomers found as donor and Ti16O32 as an acceptor in nPy-Ti16O32 composites. Sensitivity and selectivity of polypyrrole (PPy) towards NH3, CO2 and CO have been studied at DFT. PPy oligomers are used both, in the doped (PPy+) and neutral (PPy) form, for their sensing abilities to realize the best state for gas sensing. Interaction energies and amount of charges (NBO and Mulliken charge analysis) are simulated which reveal the sensing ability of PPy towards these gases. PPy, both in doped and neutral state, is more sensitive to NH3 compared to CO2 and CO. More interestingly, NH3 causes doping of PPy and de-doping of PPy+, providing evidence that PPy/PPy+ is an excellent sensor for NH3 gas. UV-vis and UV-vis-near-IR spectra of nPy, nPy+, and nPy/nPy+-X complexes demonstrate strong interaction of PPy/PPy+ with these atmospheric gases. The applications of graphene (GR) and its derivatives in the field of composite materials for solar energy conversion, energy storage, environment purification and biosensor applications have been reviewed. The vast coverage of advancements in environmental applications of GR-based materials for photocatalytic degradation of organic pollutants, gas sensing and removal of heavy metal ions is presented. Additionally, the presences of graphene composites in the bio-sensing field have been also discussed in this review.
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Wang, Siwen. « Orbital Level Understanding of Adsorbate-Surface Interactions in Metal Nanocatalysis ». Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/98923.
Texte intégralRésumé :
We develop a theoretical framework for a priori estimation of catalytic activity of metal nanoparticles using geometry-based reactivity descriptors of surface atoms and kinetic analysis of reaction pathways at various types of active sites. We show that orbitalwise coordination numbers 𝐶𝑁α (α = 𝑠 or 𝑑) can be used to predict chemical reactivity of a metal site (e.g., adsorption energies of critical reaction intermediates) by being aware of the neighboring chemical environment, outperforming their regular (𝐶𝑁) and generalized (𝐶̅𝑁̅) counterparts with little added computational cost. Here we include two examples to illustrate this method: CO oxidation on Au (5𝑑¹⁰6𝑠¹) and O₂ reduction on Pt (5𝑑⁹6𝑠¹). We also employ Bayesian learning and the Newns-Anderson model to advance the fundamental understanding of adsorbate-surface interactions on metal nanocatalysts, paving the path toward adsorbate-specific tuning of catalysis.Doctor of Philosophy
The interactions between reaction intermediates and catalysts should be neither too strong nor too weak for catalytic optimization. This Sabatiers principle arising from the scaling relations among the energetics of reacting species at geometrically similar sites, provides the conceptual basis for designing improved catalysts, but imposes volcano-type limitations on the attainable catalytic activity and selectivity. One of the greatest challenges faced by the catalysis community today is how to develop design strategies and ultimately predictive models of catalytic systems that could circumvent energy scaling relations. This work brings the quantum-chemical modeling and machine learning technique together and develops a novel stochastic modeling approach to rationally design the catalysts with desired properties and bridges our knowledge gap between the empirical kinetics and atomistic mechanisms of catalytic reactions.
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Moore, Corell H. « Modeling the peak absorption of MEH-PPV in various solvents using Density Functional Theory ». VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/6041.
Texte intégralRésumé :
Density Functional Theory (DFT) and time-dependent Density Functional Theory (TD-DFT) are powerful tools for modeling orbital energy in conjugated molecules and have been useful tools for research in organic photovoltaics. In this work, DFT is first used to explain the red shift in the absorption spectrum and increased absorption observed in MEH-PPV. Initially, the modeling of the red-shift in the absorption peak of MEH-PPV is studied using Gaussian 03 software with the global hybrid functional B3LYP for exchange-correlation and the 6-31G basis set. DFT and TD-DFT are used to separately study the effects of polymer chain length, carbon-carbon double-bond stretching, and the polymer in solution vs. in gas space on red shift in absorption spectrum.
Next, Gaussian 09 software and the same B3LYP functional and 6-31G basis set are used to study interchain and intrachain interactions of MEH-PPV in solution. The red shift in the absorption peaks for three MEH-PPV configurations (single-chain pentamer, two stacked pentamers, and decamer) are compared with experimental results for five different solvents (chloroform, toluene, xylene, dichloromethane, and chlorobenzene). This investigation indicates that inter-chain interactions dominate in “good” aromatic solvents as compared to “poor” non-aromatic solvents. The results suggest that inter-chain charge transfer interactions play a critical role in real solutions and inter-chain aggregation takes precedence over intra-chain aggregation in aromatic solvents.
In the final section of the study, accurate values for the range-separation parameter (w) for three lengths of MEH-PPV polymer (trimer, tetramer, and pentamer) in five different solvents (chloroform, chlorobenzene, xylene, Tetrahydrofuran, and dichloromethane) are reported using the range-separated functionals wB97XD and CAM-B3LYP. Using these data, range separation parameters are predicted and used for longer polymer chains in chloroform solution. The differences in the range separation parameters for the different solvents is statistically significant and gives further insight into the polymer/solvent interaction.
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Wang, Jiaqi. « Transition Metal Catalyzed Oxidative Cleavage of C-O Bond ». Thesis, University of North Texas, 2015. https://digital.library.unt.edu/ark:/67531/metadc801914/.
Texte intégralRésumé :
The focus of this thesis is on C-O bonds activation by transition metal atoms. Lignin is a potential alternative energy resource, but currently is an underused biomass species because of its highly branched structure. To aid in better understanding this species, the oxidative cleavage of the Cβ-O bond in an archetypal arylglycerol β-aryl ether (β–O–4 Linkage) model compound of lignin with late 3d, 4d, and 5d metals was investigated. Methoxyethane was utilized as a model molecule to study the activation of the C-O bond. Binding enthalpies (ΔHb), enthalpy formations (ΔH) and activation enthalpies (ΔH‡) have been studied at 298K to learn the energetic properties in the C-O bond cleavage in methoxyethane. Density functional theory (DFT) has become a common choice for the transition metal containing systems. It is important to select suitable functionals for the target reactions, especially for systems with degeneracies that lead to static correlation effects. A set of 26 density functionals including eight GGA, six meta-GGA, six hybrid-GGA, and six hybrid-meta-GGA were applied in order to investigate the performance of different types of density functionals for transition metal catalyzed C-O bond cleavage. A CR-CCSD(T)/aug-cc-pVTZ was used to calibrate the performance of different density functionals.
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Atalla, Viktor [Verfasser], Matthias [Akademischer Betreuer] Scheffler et Andreas [Akademischer Betreuer] Knorr. « Density-functional theory and beyond for organic electronic materials / Viktor Atalla. Gutachter : Andreas Knorr. Betreuer : Matthias Scheffler ». Berlin : Technische Universität Berlin, 2013. http://d-nb.info/1065665342/34.
Texte intégral
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Idziak, Christopher. « The application of density functional theory for understanding organic reactivity : nitration, super electrophiles, iridium catalysts, methanol formation ». Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=23622.
Texte intégralRésumé :
In this thesis, the ability of modern density functional theory to model organic reaction mechanisms is examined. The insights that can be obtained from computational chemistry range from the very nature of the mechanisms - the fundamental forces that drive the reaction forward - through to the role of the environment and the properties of the resulting molecules. However, the importance of these insights is most readily displayed through their application to challenging experimental problems. Therefore, the projects that are described in this work are all associated with experimental studies that are in a position to utilise the insights obtained. In the study on the nitration of 6-chloropyrimidine-4(3H)-one (Chapter 3), it was shown that the inductive effect can be employed in some instances to provide a mechanistic explanation for reactivity. This was observed to be relevant where there is a moiety within the molecule, which either withdraws or donates electronic density from or to this group. In the study on the superelectrophilic activation in amidine dications (Chapter 4), it was shown that relative energetics with respect to formation of reactant/product complexes and transition states can be influenced by the presence or absence of associated counterions. In the study on the use of iridium based catalysts for hydrogen isotope exchange (Chapter 5) the role of solvent molecules in affecting the reactivity was assessed. This study led to the rationalization and selection of a preferred and beneficial solvent for carrying out these reactions. In the formation of methanol from CO and CO2 (Chapter 6) an explanation in terms of relative energetic changes of a series of steps in a novel route to Methanol formation has been reported. It has been shown that the relative energetics of these set of reactions are within a satisfactory range for the process to proceed as represented experimentally.
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Artuc, Zuleyha. « Density Functional Theory Investigation Of Noble Metal Reduction Agents On Gamma-al2o3 In Nox Storage/reduction Catalysis ». Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613756/index.pdf.
Texte intégralRésumé :
Pollution from automobile exhaust is one of the most major environmental problems because of increasing usage of engine technologies. Diesel and lean burn gasoline engines operate
under oxygen rich (lean) conditions and they emit harmfull gases to the atmosphere (CO,CO2, NO, NO2). The control of NOx emission from exhaust has become a challenging issue
in engine industry because of the worldwide environmental regulations. Therefore lean-burn NOx emission control technologies have been developed to reduce emission of harmfull gases from exhausts, and the NOx storage/reduction (NSR) catalysts is one of the most promising candidates to reduce the pollution caused by lean-burn engines. In NSR systems, NO from the emission is first oxidized to NO2 over noble metal sites (Pt, Rh, Pd) during lean-burn engine operation. After that NO2 is stored as nitrites and nitrates in alkali earth oxides (BaO,MgO, CaO) particles or monolayer which is well dispersed on a substrate (Gamma-Al2O3, TiO2,
SiO2). Finally, stored NOx compound are broken into N2 and O2 on noble metal sites. The Pt/BaO/Gamma-Al2O3 system is one of the most popular subjects in literature both experimentally and theoretically since this system is known to be catalytically more active and ecient in interactions between NOx and Pt-BaO components are still not clearly explained. For this reason, in this thesis, the interaction between catalytic redox components, Pt and Rh, and the support material
Gamma-Al2O3 and the eects of Pt and Rh in atomic and diatomic clusters forms on the adsorption of the NO2 molecule on the Gamma-Al2O3(100) surface have been investigated
by using density functional theory (DFT).
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Zelazny, Mateusz Aleksander. « An investigation into vibrational dynamics in organic semiconductors ». Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/284209.
Texte intégralRésumé :
This thesis is concerned with study of vibrational dynamics and their effect on charge transport in thin films of organic semiconductors. Two classes of organic semiconductors are investigated- crystalline small molecules and conjugated polymers. Although device performance of both classes of materials has greatly improved over last two decades, detailed understanding of relationship between structure and transport properties is still missing- so far development of organic semiconductors has mostly been based on experimental approach, with theoretical models providing post factum justification rather than guiding rational design of novel compounds. In this thesis I establish methodology to investigate both inter- and intramolecular vibrational modes by combining latest computational techniques with experimental pressure-dependent Raman spectroscopy. The dominant factor limiting charge delocalization in crystalline small molecules are low frequency, large amplitude intermolecular modes. However, theoretical modeling of these modes require use of periodic boundary conditions increasing computational cost by orders of magnitude when compared to commonly used vacuum phase simulations. I report comparative study of two implementations (CRYSTAL09 and CASTEP) of density functional theory (DFT) and dispersion correction (Grimme and Tkatchenko-Scheffler) and evaluate their applicability to predict low frequency vibrational modes in 2,7-Dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) and 2,8-Difl uoro-5,11-bis(triethylsilylethynyl)anthradithiophene (dif-TES-ADT). Charge transport in conjugated polymers is strongly affected by energetic disorder arising from spatial variations in backbone conformation. I combine vacuum phase DFT simulations of intramolecular vibrational modes with pressure-dependent Raman spectroscopy to study planarity and torsional backbone disorder of 2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene (pBTTT), indacenodithiophene-co-benzo-thiadiazole (IDT-BT), diketopyrrolopyrrole-benzotriazole (DPP-BTZ) and naphtalene-bithiophene (NDI-T2) at pressures up to 3.9 GPa. It is shown that Raman spectra of pBTTT and NDI-T2 demonstrate dependence of mode intensities on hydrostatic pressure, whereas spectra of IDT-BT and DPP-BTZ exhibit lack of dependence. Simulations of theoretical spectra performed as a function of backbone torsion indicate that pBTTT undergoes deplanarization of already non-planar backbone and that NDI-T2 backbone is planarized, whereas backbones of IDT-BT and DPP-BTZ are resilient to changes of conformation. Finally, I perform large scale molecular dynamics simulations of crystalline, semi-crystalline and disordered phases of IDT-BT and DPP-BT in order to investigate effect of disorder on backbone conformation. Both compounds were previously reported to exhibit extremely low degree of energetic disorder- I assign this phenomenon to their surprisingly strong resilience to side chain disorder. In both systems simulations demonstrate novel mechanism of disorder accommodation- their backbones bend rather than twist and retain low degree of torsional variation even in amorphous phase.
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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.
Texte intégralRésumé :
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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Nicholson, Kelly Marie. « First principles calculations of thermodynamics of high temperature metal hydrides for NGNP applications ». Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54027.
Texte intégralRésumé :
In addition to their potential use at low to moderate temperatures in mobile fuel cell technologies, metal hydrides may also find application as high temperature tritium getterers in the U.S. DOE Next Generation Nuclear Plant (NGNP). We use Density Functional Theory to identify metal hydrides capable of sequestering tritium at temperatures in excess of 1000 K. First we establish the minimum level of theory required to accurately capture the thermodynamics of highly stable metal hydrides and determine that isotope effects can be neglected for material screening. Binary hydride thermodynamics are largely well established, and ternary and higher hydrides typically either do not form or decompose at lower temperatures. In this thesis we investigate anomalous systems with enhanced stability in order to identify candidates for the NGNP application beyond the binary hydrides. Methods implemented in this work are particularly useful for deriving finite temperature phase stability behavior in condensed systems. We use grand potential minimization methods to predict the interstitial Th−Zr−H phase diagram and apply high throughput, semi-automated screening methodologies to identify candidate complex transition metal hydrides (CTMHs) from a diverse library of all known, simulation ready ternary and quaternary CTMHs (102 materials) and 149 hypothetical ternary CTMHs based on existing prototype structures. Our calculations significantly expand both the thermodynamic data available for known CTMHs and the potential composition space over which previously unobserved CTMHs may be thermodynamically stable. Initial calculations indicate that the overall economic viability of the tritium sequestration system for the NGNP will largely depend on the amount of protium rather than tritium in the metal hydride gettering bed feed stream.
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Dain, Ryan P. « Investigation of gas-phase metal ion complexes using infrared multiple photon dissociation spectroscopy and density functional theory calculations ». Thesis, Wichita State University, 2010. http://hdl.handle.net/10057/3300.
Texte intégralRésumé :
A combination of theoretical chemistry and “action” spectroscopy has become the most
used tool for the exploration of gas-phase molecular ions. In this study, density functional theory
(DFT) calculations were used to test the validity of conclusions drawn from the results of a
matrix-isolation infrared (MI-IR) experiment and develop a modeling method that could be used
for metal-coordinating chlorate ion pairs. That modeling method was then used in comparison
with experimental infrared multiple photon dissociation (IRMPD) spectroscopy to determine the
structures of metal-chlorate anions. In addition to structural information, the effect of the
modeling method on spectral correlation was also investigated.Thesis (M.S.)--Wichita State University, College of Liberal Arts and Sciences, Dept. of Chemistry
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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/.
Texte intégralRésumé :
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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Dutta, Debosruti. « Insights into the Epitaxial Relationships between One-Dimensional Nanomaterials and Metal Catalyst Surfaces Using Density Functional Theory Calculations ». Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5213.
Texte intégralRésumé :
This dissertation involves the study of epitaxial behavior of one-dimensional nanomaterials like single-walled carbon nanotubes and Indium Arsenide nanowires grown on metallic catalyst surfaces. It has been previously observed in our novel microplasma based CVD growth of SWCNTs on Ni-Fe bimetallic nanoparticles that changes in the metal catalyst composition was accompanied by variations in the average metal-metal bond lengths of the nanoparticle and that in turn, affected nanotube chirality distributions. In this dissertation, we have developed a very simplistic model of the metal catalyst in order to explain the nanotube growth of specific nanotube chiralities on various Ni-Fe catalyst surfaces. The metal catalyst model is a two-dimensional flat surface with varying metal-metal bond lengths and comprising of constituent metal atoms. The effect of the composition change was modeled as a change in the bond length of the model catalyst surface and density functional theory based calculations were used to study specific nanotube caps. Our results indicated that nanotube caps like (8,4) and (6,5) show enhanced binding with increased metal-metal bond lengths in the nanoparticle in excellent agreement with the experimental observations. Later, we used this epitaxial nucleation model and combined with a previously proposed chirality-dependent growth rate model to explore better catalysts that will preferentially grow an enhanced chirality distribution of metallic nanotubes. From our DFT calculations and other geometrical considerations for nanotube growth, we demonstrated that the pure Ni0.5Cu0.5 metal nanoparticles and its lattice-strained surfaces can serve as a promising catalyst for enhanced growth of metallic nanotubes. Finally, we extended this model of epitaxial growth to study the growth of,andoriented nanowires on gold metal nanoparticles where a faster growth rate ofnanowires was previously observed in experiments on shaped nanoparticles than that on spherical nanoparticles. The DFT calculations indicated an enhanced growth selectivity of theoriented nanowires on the Au(111) surfaces. However, the DFT results also show that theandNWs will preferentially grow on the Au(100) surface than on the Au(100) surface. The epitaxial model based DFT calculations of nanotube and nanowire growth on metal catalyst surfaces presented in this dissertation, provide a deep insight into their epitaxial growth mechansims and, can be easily exploited to layout better design principles of synthesizing catalysts that helps in growing these one-dimensional nanomaterials with desired material properties.
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Martin, Claudia. « Density functional study of the electronic and magnetic properties of selected transition metal complexes ». Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2014. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-134958.
Texte intégralRésumé :
Die vorliegende Promotionsarbeit “Density functional study of the electronic and magnetic properties of selected transition metal complexes” beschäftigt sich mit dem Zusammenhang zwischen strukturellen Merkmalen sowie elektronischen und magnetischen Eigenschaften von Einzelmolekül-Magneten. Im Wesentlichen konnte dabei gezeigt werden, dass die magnetischen Eigenschaften sowohl von strukturellen Merkmalen als auch von den elektronischen Eigenschaften bestimmt werden. Des Weiteren ergab sich, dass verschiedene Kenngrößen der magnetischen Eigenschaften (im speziellen der magnetische Grundzustand S sowie die magnetische Anisotropie D) miteinander korreliert sind. Dies ist im Besonderen für eine mögliche Anwendung von Einzelmolekül-Magneten im Bereich der Datenspeicherung von Bedeutung.
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Weerawardene, K. L. Dimuthu M. « Optical and luminescence properties of noble metal nanoparticles ». Diss., Kansas State University, 2017. http://hdl.handle.net/2097/38189.
Texte intégralRésumé :
Doctor of PhilosophyDepartment of Chemistry
Christine M. Aikens
The remarkable optical and luminescence properties of noble metal nanoparticles (with diameters < 2 nm) attract researchers due to potential applications in biomedicine, photocatalysis, and optoelectronics. Extensive experimental investigations on luminescence properties of thiolate-protected gold and silver nanoclusters during the past decade have failed to unravel their exact photoluminescence mechanism. Herein, density functional and time-dependent density functional theory (DFT and TDDFT) calculations are performed to elucidate electronic-level details of several such systems upon photoexcitation. Multiple excited states are found to be involved in photoemission from Au₂₅(SR)₁₈– nanoclusters, and their energies agree well with experimental emission energies. The Au₁₃ core-based excitations arising due to electrons excited from superatom P orbitals into the lowest two superatom D orbitals are responsible for all of these states. The large Stokes shift is attributed to significant geometrical and electronic structure changes in the excited state. The origin of photoluminescence of Ag₂₅(SR)₁₈– nanoclusters is analogous to their gold counterparts and heteroatom doping of each cluster with silver and gold correspondingly does not affect their luminescence mechanism. Other systems have been examined in this work to determine how widespread these observations are. We observe a very small Stokes shift for Au₃₈(SH)₂₄ that correlates with a relatively rigid structure with small bond length changes in its Au₂₃ core and a large Stokes shift for Au₂₂(SH)₁₈ with a large degree of structural flexibility in its Au₇ core. This suggests a relationship between the Stokes shift of gold−thiolate nanoparticles and their structural flexibility upon photoexcitation. The effect of ligands on the geometric structure and optical properties of the Au₂₀(SR)₁₆ nanocluster is explored. Comparison of the relative stability and optical absorption spectra suggests that this system prefers the [Au₇(Au₈SR₈)(Au₃SR₄)(AuSR₂)₂] structure regardless of whether aliphatic or aromatic ligands are employed. The real-time (RT) TDDFT method is rapidly gaining prominence as an alternative approach to capture optical properties of molecular systems. A systematic benchmark study is performed to demonstrate the consistency of linear-response (LR) and RT-TDDFT methods for calculating the optical absorption spectra of a variety of bare gold and silver nanoparticles with different sizes and shapes.
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Kuhlman, Andrew. « An Ab-Initio Study on the Chemical Modification of Raman Spectra of Organic Adsorbates on Semiconductor Surfaces ». Bowling Green State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1402334244.
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Oymak, Huseyin. « Theoretical Investigation Of Altini Ternary Clusters : Density Functional Theory Calculations And Molecular Dynamics Simulations ». Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605104/index.pdf.
Texte intégralRésumé :
This doctoral study consists of three parts. In the first part, structural and electronic properties of Al_kTi_lNi_m (k+l+m=2,3) microclusters have been investigated by performing density functional theory (DFT) calculations within the B3LYP [which comprises the Becke-88 exchange functional and the correlation functional of Lee, Yang, and Parr] and the effective core potential (ECP) level. Dimers and trimers of the elements aluminum, titanium, and nickel, and their binary and ternary combinations have been studied in their ground states. The optimum geometries, possible dissociation channels, vibrational properties, and electronic structure of the clusters under study have been obtained.
In the second part, after an empirical potential energy function (PEF) has been parametrized for the AlTiNi ternary system, stable (minimum-energy) structures of Al_kTi_lNi_m (k+l+m=4) microclusters have been determined by molecular dynamics (MD) simulations. The energetics of the microclusters in 1K and 300 K have been discussed. By performing, again, DFT calculations (within the B3LYP and ECP level), the possible dissociation channels and electronic properties of the obtained clusters have been calculated.
In the last part, using the empirical PEF parametrized previously for the AlTiNi ternary system, minimum-energy structures of Al_nTi_nNi_n (n= 1-16) ternary alloy nanoparticles have been determined by performing MD simulations. The structural and energetic features of the obtained nanoparticles have been investigated.