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1
Östlin, Andreas. "Electronic structure studies and method development for complex materials". Doctoral thesis, KTH, Tillämpad materialfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-167109.
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Over the years electronic structure theory has proven to be a powerful method with which one can probe the behaviour of materials, making it possible to describe and predict material properties. The numerical tools needed for these methods are always in need of development, since the desire to calculate more complex materials pushes this field forward. This thesis contains work on both this implementational and developmental aspects. It begins by reviewing density functional theory and dynamical mean field theory, with the aim of merging these two methods. We point out theoretical and technical issues that may occur while doing this. One issue is the Padé approximant, which is used for analytical continuation. We assess the approximant and point out difficulties that can occur, and propose and evaluate methods for their solution. The virial theorem is assessed within the framework of density functional theory merged with many-body methods. We find that the virial theorem is extended from its usual form, and confirm this by performing practical calculations. The unified theory of crystal structure for transition metals has been established a long time ago using early electronic structure calculations. Here we implement the first- principles exact muffin-tin orbitals method to investigate the structural properties of the 6d transition metals. The goal of our study is to verify the existing theory for the mostly unknown 6d series and the performance of the current state-of-the art in the case of heavy d metals. It is found that these elements behave similarly to their lighter counterparts, except for a few deviations. In these cases we argue that it is relativistic effects that cause this anomalous behaviour. Palladium is then studied, taking many-body effects into account. We find that we can reproduce experimental photoemission spectra by these methods, as well as the Fermi surface. The thesis ends with an investigation of the stacking fault energies of the strongly correlated metal cerium. In addition to providing the first ab-initio stacking fault data for the two cubic phases of Ce, we discuss how these results could have an impact on the interpretation of the phase diagram of ceriumQC 20150522
2
Wang, Baochang. "Electronic Structure and Optical Properties of Solar Energy Materials". Doctoral thesis, KTH, Flerskalig materialmodellering, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-145625.
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In this thesis, we have studied the electronic and optical properties of solar energy m-terials. The studies are performed in the framework of density functional theory (DFT), GW, Bethe-Salpeter equation (BSE) approaches and Kinetic Monte Carlo (KMC). We present four sets of results. In the first part, we report our results on the band gap engineering issues for BiNbO4and NaTaO3, both of which are good photocatalysts. The band gap tuning is required for these materials in order to achieve the maximum solar to hydrogen conversion efficiency. The most common method for the band gap reduction is an introduction of foreign elements. The mono-doping in the system generates electrons or holes states near band edges, which reduce the efficiency of photocatalytic process. Co-doping with anion and cation or anion and anion can provide a clean band gap. We have shown that further band gap reduction can be achieved by double-hole mediated coupling between two anionic dopants. In the second part, the structure and optical properties of (CdSxSe1x)42nanoclusters have been studied. Within this study, the structures of the (CdS)42, (CdSe)42, Cd42Se32S10, Cd42Se22S20, and Cd42Se10S32 clusters have been determined using the simulated annealing method. Factors influencing the band gap value have been analyzed. We show that the gap is most significantly reduced when strongly under coordinated atoms are present on the surface of the nanoclusters. In addition, the band gap depends on the S concentration as well as on the distribution of the S and Se atoms in the clusters. We present the optical absorption spectra calculated with BSE and random phase approximation (RPA) methods based on the GW corrected quasiparticle energies. In the third part, we have employed the state-of-art computational methods to investigate the electronic structure and optical properties of TiO2high pressure polymorphs. GW and BSE methods have been used in these calculations. Our calculations suggest that the band gap of fluorite and pyrite phases have optimal values for the photocatalytic process of decomposing water in the visible light range. In the fourth part we have built a kinetic model of the first water monolayer growth on TiO2(110) using the kinetic Monte Carlo (KMC) method based on parameters describing water diffusion and dissociation obtained from first principle calculations. Our simulations reproduce the experimental trends and rationalize these observations in terms of a competition between different elementary processes. At high temperatures our simulation shows that the structure is well equilibrated, while at lower temperatures adsorbed water molecules are trapped in hydrogen-bonded chains around pairs of hydroxyl groups, causing the observed higher number of molecularly adsorbed species at lower temperature.QC 20140603
3
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.
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Lu, Haichang. "Electronic structure, defect formation and passivation of 2D materials". Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/284926.
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The emerging 2D materials are potential solutions to the scaling of electronic devices to smaller sizes with lower energy cost and faster computing speed. Unlike traditional semiconductors e.g. Si, Ge, 2D materials do not have surface dangling bonds and the short-channel effect. A wide variety of band structure is available for different functions. The aim of the thesis is to calculate the electronic structures of several important 2D materials and study their application in particular devices, using density functional theory (DFT) which provides robust results. The Schottky barrier height (SBH) is calculated for hexagonal nitrides. The SBH has a linear relationship with metal work function but the slope does not always equal because Fermi level pinning (FLP) arises. The chemical trend of FLP is investigated. Then we show that the pinning factor of Si can be tuned by inserting an oxide interlayer, which is important in the application to dopant-free Si solar cells. Apart from contact resistance, we want to improve the conductivity of the electrode. This can be done by using a physisorbed contact layer like FeCl3, AuCl3, and SbF5 etc. to dope the graphene without making the graphene pucker so these dopants do not degrade the graphene's carrier mobility. Then we consider the defect formation of 2D HfS2 and SnS2 which are candidates in the n-type part of a tunnel FET. We found that these two materials have high mobility but there are also intrinsic defects including the S vacancy, S interstitial, and Hf/Sn interstitial. Finally, we study how to make defect states chemically inactive, namely passivation. The S vacancy is the most important defect in mechanically exfoliated 2D MoS2. We found that in the most successful superacid bis(trifluoromethane) sulfonamide (TFSI) treatment, H is the passivation agent. A symmetric adsorption geometry of 3H in the -1 charge state can remove all gap states and return the Fermi level to the midgap.
5
Zhang, Chunmei. "Computational discovery and design of novel materials from electronic structure engineering". Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/149858/1/Chunmei_Zhang_Thesis.pdf.
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This thesis studied the electronic structure of materials based on density functional theory calculations and theoretical tight-binding modelling. Besides the electronic structure for pure two-dimensional and three-dimensional materials, this research also explored the new physics in the interface and surface of those materials. In doing so, this thesis discovered and designed a series of novel materials which can be used in nanoelectronics, optoelectronics, information storage, as well as energy storage.↲
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Ramzan, Muhammad. "Structural, Electronic and Mechanical Properties of Advanced Functional Materials". Doctoral thesis, Uppsala universitet, Materialteori, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-205243.
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The search for alternate and renewable energy resources as well as the efficient use of energy and development of such systems that can help to save the energy consumption is needed because of exponential growth in world population, limited conventional fossil fuel resources, and to meet the increasing demand of clean and environment friendly substitutes. Hydrogen being the simplest, most abundant and clean energy carrier has the potential to fulfill some of these requirements provided the development of efficient, safe and durable systems for its production, storage and usage. Chemical hydrides, complex hydrides and nanomaterials, where the hydrogen is either chemically bonded to the metal ions or physiosorbed, are the possible means to overcome the difficulties associated with the storage and usage of hydrogen at favorable conditions. We have studied the structural and electronic properties of some of the chemical hydrides, complex hydrides and functionalized nanostructures to understand the kinetics and thermodynamics of these materials. Another active field relating to energy storage is rechargeable batteries. We have studied the detailed crystal and electronic structures of Li and Mg based cathode materials and calculated the average intercalation voltage of the corresponding batteries. We found that transition metal doped MgH2 nanocluster is a material to use efficiently not only in batteries but also in fuel-cell technologies. MAX phases can be used to develop the systems to save the energy consumption. We have chosen one compound from each of all known types of MAX phases and analyzed the structural, electronic, and mechanical properties using the hybrid functional. We suggest that the proper treatment of correlation effects is important for the correct description of Cr2AlC and Cr2GeC by the good choice of Hubbard 'U' in DFT+U method. Hydrogen is fascinating to physicists due to predicted possibility of metallization and high temperature superconductivity. On the basis of our ab initio molecular dynamics studies, we propose that the recent claim of conductive hydrogen by experiments might be explained by the diffusion of hydrogen at relevant pressure and temperature. In this thesis we also present the studies of phase change memory materials, oxides and amorphization of oxide materials, spintronics and sulfide materials.
7
Hansson, Anders. "Electronic Structure and Transport Properties of Carbon Based Materials". Doctoral thesis, Linköpings universitet, Beräkningsfysik, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-7544.
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In the past decade the interest in molecular electronic devices has escalated. The synthesis of molecular crystals has improved, providing single crystals or thin films with mobility comparable with or even higher than amorphous silicon. Their mechanical flexibility admits new types of applications and usage of electronic devices. Some of these organic crystals also display magnetic effects. Furthermore, the fullerene and carbon nanotube allotropes of carbon are prominent candidates for various types of applications. The carbon nanotubes, in particular, are suitable for molecular wire applications with their robust, hollow and almost one-dimensional structure and diverse band structure. In this thesis, we have theoretically investigated carbon based materials, such as carbon nanotubes, pentacene and spiro-biphenalenyl neutral radical molecular crystals. The work mainly deals with the electron structure and the transport properties thereof. The first studies concerns effects and defects in devices of finite carbon nanotubes. The transport properties, that is, conductance, are calculated with the Landauer approach. The device setup contains two metallic leads attached to the carbon nanotubes. Structural defects as vacancies and bending are considered for single-walled carbon nanotubes. For the multi-walled carbon nanotubes the focus is on inter-shell interaction and telescopic junctions. The current voltage characteristics of these systems show clear marks of quantum dot behaviour. The influence of defects as vacancies and geometrical deformations are significant for infinite systems, but in these devices they play a minor role. The rest of the studies concern molecular crystals, treated with density-functional theory (DFT). Inspired by the enhance of the electrical conductivity obtained experimentally by doping similar materials with alkali metals, calculations were performed on bundles of single-walled carbon nanotubes and pentacene crystals doped with potassium. The most prominent effect of the potassium intercalation is the shift of Fermi level in the nanotube bands. A sign of charge transfer of the valence electrons of the potassium atoms. Semi-conducting bundles become metallic and metallic bundles gain density of states at the Fermi level. In the semi-conducting pristine pentacene crystals structural transitions occur upon doping. The herringbone arrangement of the pristine pentacene molecules relaxes to a more π-stacked structure causing more dispersive bands. The charge transfer shifts the Fermi level into the lowest unoccupied molecular orbital band and turns the crystal metallic. Finally, we have studied molecular crystals of spiro-biphenalenyl neutral radicals. According to experimental studies, some of these materials show simultaneous electrical, optical and magnetical bistability. The electronic properties of these crystals are investigated by means of DFT with a focus on the possible intermolecular interactions of radical spins.
8
Li, Zhi. "Electronic Structure Characterization of Hybrid Materials". Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5060.
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In this dissertation, the studies aim to characterize the electronic structure at the internal interface of hybrid materials. The characterization challenge is originating from the spectral superposition of hybrid constituents. A characterization protocol based on photoemission spectroscopy (PES) was developed and applied to investigate the orbital alignment at the internal interface of the oligothiophene-TiO2 and ArS-CdSe hybrid materials by characterizing the individual constituents and the assembly hybrids respectively. Electrospray deposition technique was used to deposit targeting materials which enabled preparation of thin films in vacuum minimizing ambient contaminations while transmission electron microscopy (TEM) was used to investigate the morphology and the particle size of the pure nanoparticles and the hybrids. Ultraviolet-visible (UV-vis) spectroscopy was also used in the estimation of the optical band gap of the pure nanoparticles and the HOMO-LUMO gap of the organic ligands.
One of the hybrid materials studied in this dissertation is oligothiophene-TiO2 nanoparticle hybrids in which the oligothiophene ligands are bonded to the surface of TiO2 nanoparticles covalently. This hybrid system was used to develop and demonstrate a measurement protocol to characterize the orbital alignment at the internal interface. Low intensity X-ray photoemission spectroscopy (LIXPS) was used to determine the work function of the oligothiophene ligands and the TiO2 nanoparticles. In combination with the highest occupied molecular orbital (HOMO) cutoff and the valence band maximum (VBM) measured by ultraviolet photoemission spectroscopy (UPS), the ionization energies (IE) of these two constituents were determined. X-ray photoemission spectroscopy (XPS) was used to characterize the core level emissions of the constituents and the hybrid assembly, which were used to determine the charge injection barriers at the internal interface.
The results showed that there was an interface dipole at the internal interface between organic and inorganic constituents of the hybrid. The dipole was determined to be 0.61 eV and the hole injection barrier at the internal interface amounted to 0.73 eV. The electron injection barrier was estimated by taking into account the gap between highest occupied and lowest unoccupied molecular orbitals (HOMO, LUMO). The procedure followed only suggested the presence of an insignificant barrier in the oligothiophene-TiO2 nanoparticle hybrids.
Arylthiol functionalized Cadmium Selenide (ArS-CdSe) is a novel hybrid material which can be used in hetero-junction solar cells. The ArSH ligands are bonded on the surface of the CdSe nanoparticles covalently through sulfur atoms serving as anchors. The internal interface in the ArS-CdSe hybrids between the organic constituent and the inorganic constituent was studied by the same characterization protocol developed in this dissertation. Furthermore, a physisorbed interface between the ArSH ligands and the CdSe nanoparticles was created through multi-step in-vacuum deposition procedure. The electrospray deposition technique enabled the formation of a well-defined physisorbed interface which was characterized by LIXPS, UPS and XPS for each deposition step. Accordingly, the orbital alignment at the physisorbed interface was determined.
Based on the results obtained, detailed orbital alignments at the ArSH/CdSe physisorbed interface and the internal interface in the ArS-CdSe hybrid materials were delineated and discussed. The hole injection and electron injection barrier at the physisorbed ArSH/CdSe interface are 0.7 eV and 1.0 eV respectively. An interface dipole of 0.4 eV was observed at the interface. In the ArS-CdSe hybrid materials, the electronic system of the ArSH component shifts down due to the charge transfer induced by the covalent hybridization. The hybridization also shifts the electronic system of the CdSe constituent to a lower energy level due to saturation of the unoccupied bonds of the Cd atoms on the surface. The hole injection barrier and electron injection barrier were determined to be 0.5 eV and 1.2 eV respectively. A small interface dipole (0.2 eV) was observed at the internal interface as a result of the presence of covalent bonds.
9
Dziekan, Thomas. "Electronic Transport in Strained Materials". Doctoral thesis, Uppsala University, Department of Physics and Materials Science, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8471.
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In this thesis the conductivity of strained materials has been investigated using density functional theory and a semiclassical transport theory based on the Boltzmann equation.
In transition metals trends are reproduced without adjustable parameters. The introduction of one temperature dependent cross section allowed the reproduction of resistivity trends between 10 and 1000K.
The effect of strain on transition metals in bcc and fcc structure was studied deforming the unit cell along the tetragonal deformation path. The anisotropy of the conductivity varied on wide range of the c/a-ratio. The orbitals at the Fermi level determined the principal behavior. Pairs of elements with permutated number of electrons and holes in the 4d band showed similar behavior. The concept of the tetragonal deformation was also applied on semiconductors.
The deformation of Vanadium in X/V superlattices (X=Cr,~Fe,~Mo) due to Hydrogen loading depends on the properties of X. It was found that counteracting effects due to the presence of Hydrogen influence the conductivity.
It is shown that a small magnetic moment of the V host reduces the hydrogen solubility. Depending on the magnitude of the tetragonal distortion of V, the hydrogen dissolution becomes favored for larger moments.
Finally, extra charge filling of the bandstructure of Cr and Mo decreases the Fermi velocity and increases the density of states at the Fermi energy.
10
Baum, Zachary John. "Reactivity of Tetraborylmethanes and Electronic Structure Calculations of Dimensionally Reduced Materials". The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1531736836448112.
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Hugosson, Håkan Wilhelm. "A Theoretical Treatise on the Electronic Structure of Designer Hard Materials". Doctoral thesis, Uppsala University, Department of Physics, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-651.
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The subject of the present thesis is theoretical first principles electronic structure calculations on designer hard materials such as the transition metal carbides and oxides. The theoretical investigations have been made in close collaboration with experimental research and have addressed both bulk electronic properties and surface electronic properties of the materials.
Among the bulk studies are investigations on the effects of substoichiometry on the relative phase stabilities and the electronic structure of several phases of MoC and the nature of the resulting vacancy peaks. The changes in phase stabilities and homo-geneity ranges in the group IV to VI transition metal carbides have been studied and explained, from calculations of the T=0 energies of formation and cohesive energies. The anomalous volume behavior and phase stabilities in substoichiometric TiC was studied including effects of local relaxations around the vacancy sites. The vacancy ordering problem in this compound was also studied by a combination of electronic structure calculations and statistical physics.
The studies of the surface electronic properties include research on the surface energies and work functions of the transition metal carbides and an investigation on the segregation of transition metal impurities on the TiC (100) surface.
Theoretical studies with the aim to facilitate the realization of novel designer hard materials were made, among these a survey of means of stabilizing potentially super-hard cubic RuO2, studying the effects of alloying, substoichiometry and lattice strains. A mechanism for enhancing hardness in the industrially important hard transition metal carbides and nitrides, from the discovery of multi-phase/polytypic alloys, has also been predicted from theoretical calculations.
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Ikeda, Yuji. "Theoretical Studies of Electronic Structures and Conductive Properties of Functional Materials". 京都大学 (Kyoto University), 2013. http://hdl.handle.net/2433/174881.
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Fukushima, Akinori. "Theoretical Studies of Electronic Structures and Dielectric Properties of Functional Materials". 京都大学 (Kyoto University), 2011. http://hdl.handle.net/2433/142172.
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Locht, Inka L. M. "Theoretical methods for the electronic structure and magnetism of strongly correlated materials". Doctoral thesis, Uppsala universitet, Materialteori, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-308699.
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In this work we study the interesting physics of the rare earths, and the microscopic state after ultrafast magnetization dynamics in iron. Moreover, this work covers the development, examination and application of several methods used in solid state physics. The first and the last part are related to strongly correlated electrons. The second part is related to the field of ultrafast magnetization dynamics. In the first part we apply density functional theory plus dynamical mean field theory within the Hubbard I approximation to describe the interesting physics of the rare-earth metals. These elements are characterized by the localized nature of the 4f electrons and the itinerant character of the other valence electrons. We calculate a wide range of properties of the rare-earth metals and find a good correspondence with experimental data. We argue that this theory can be the basis of future investigations addressing rare-earth based materials in general. In the second part of this thesis we develop a model, based on statistical arguments, to predict the microscopic state after ultrafast magnetization dynamics in iron. We predict that the microscopic state after ultrafast demagnetization is qualitatively different from the state after ultrafast increase of magnetization. This prediction is supported by previously published spectra obtained in magneto-optical experiments. Our model makes it possible to compare the measured data to results that are calculated from microscopic properties. We also investigate the relation between the magnetic asymmetry and the magnetization. In the last part of this work we examine several methods of analytic continuation that are used in many-body physics to obtain physical quantities on real energies from either imaginary time or Matsubara frequency data. In particular, we improve the Padé approximant method of analytic continuation. We compare the reliability and performance of this and other methods for both one and two-particle Green's functions. We also investigate the advantages of implementing a method of analytic continuation based on stochastic sampling on a graphics processing unit (GPU).
15
Bultmark, Fredrik. "Distorted Space and Multipoles in Electronic Structure Calculations". Doctoral thesis, Uppsala universitet, Institutionen för fysik och materialvetenskap, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9553.
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This thesis concerns methods for electronic structure calculations and some applications of the methods. The augmented planewave (APW) basis set and it’s relatives LAPW (linearised APW) and APW+lo (local orbitals) have been widely used for electronic structure calculations. Here a modification of the APW basis set based on a transformation of the basis functions from a curvilinear coordinate system. Applications to a few test systems show that the modified basis set may speed up electronic structure calculations of sparse systems. The local density approximation (LDA) is used in density functional theory. Although it is the simplest possible approximation possible for the unknown exchange-correlation energy functional, it has proven to give quite accurate results for a wide range of systems. LDA fails in systems where the non-local effects are important. By including non-local effects by adding an orbital dependent term to the energy functional, through for example the LDA+U method, the calculated properties of many materials are closer to experimental observations. In the thesis the most general formulation of the LDA+U method is presented and a new way of interpreting the results of a calculations by formulating the orbital dependent part of the energy functional in terms of multipole momentum tensors. Applications to some early actinide systems leads to a reformulations of Hund’s rules for polarisations associated with the spin and orbital magnetic moment and a suggestion for similar rules, Katt’s rules, valid in the strong spin orbit coupling regime.
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Iusan, Diana Mihaela. "Density Functional Theory Applied to Materials for Spintronics". Doctoral thesis, Uppsala universitet, Materialteori, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-119887.
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The properties of dilute magnetic semiconductors have been studied by combined ab initio, Monte Carlo, and experimental techniques. This class of materials could be very important for future spintronic devices, that offer enriched functionality by making use of both the spin and the charge of the electrons. The main part of the thesis concerns the transition metal doped ZnO. The role of defects on the magnetic interactions in Mn-doped ZnO was investigated. In the presence of acceptor defects such as zinc vacancies and oxygen substitution by nitrogen, the magnetic interactions are ferromagnetic. For dilute concentrations of Mn (~ 5%) the ordering temperature of the system is low, due to the short ranged character of the exchange interactions and disorder effects. The clustering tendency of the Co atoms in a ZnO matrix was also studied. The electronic structure, and in turn the magnetic interactions among the Co atoms, is strongly dependent on the exchange-correlation functional used. It is found that Co impurities tend to form nanoclusters and that the interactions among these atoms are antiferromagnetic within the local spin density approximation + Hubbard U approach. The electronic structure, as well as the chemical and magnetic interactions in Co and (Co,Al)-doped ZnO, was investigated by joined experimental and theoretical techniques. For a good agreement between the two, approximations beyond the local density approximation must be used. It is found that the Co atoms prefer to cluster within the semiconducting matrix, a tendency which is increased with Al co-doping. We envision that it is best to describe the system as superparamagnetic due to the formation of Co nanoclusters within which the interactions are antiferromagnetic. The magnetic anisotropy and evolution of magnetic domains in Fe81Ni19/Co(001) superlattices were investigated both experimentally, as well as using model spin dynamics. A magnetic reorientation transition was found.
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Kocevski, Vancho. "Theory and Modelling of Functional Materials". Doctoral thesis, Uppsala universitet, Materialteori, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-248513.
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The diverse field of material research has been steadily expanding with a great help from computational physics, especially in the investigation of the fundamental properties of materials. This has driven the computational physics to become one of the main branches of physics, allowing for density functional theory (DFT) to develop as one of the cornerstones of material research. Nowdays, DFT is the method of choice in a great variety of studies, from fundamental properties, to materials modelling and searching for new materials. In this thesis, DFT is employed for the study of a small part of this vast pool of applications. Specifically, the microscopic characteristics of Zn1-xCdxS alloys are studied by looking into the evolution of the local structure. In addition, the way to model the growth of graphene on Fe(110) surface is discussed. The structural stability of silicon nanocrystals with various shapes is analysed in detail, as well. DFT is further used in studying different properties of semiconductor nanocrystals. The size evolution of the character of the band gap in silicon nanocrystals is investigated in terms of changes in the character of the states around the band gap. The influence of various surface impurities on the band gap, as well as on the electronic and optical properties of silicon nanocrystals is further studied. In addition, the future use of silicon nanocrystals in photovoltaic devices is examined by studying the band alignment and the charge densities of silicon nanocrystals embedded in a silicon carbide matrix. Furthermore, the electronic and optical properties of different semiconductor nanocrystals is also investigated. In the case of the CdSe/CdS and CdS/ZnS core-shell nanocrystals the influence of the nanocrystal size and different structural models on their properties is analysed. For silicon nanocrystal capped with organic ligands, the changes in the optical properties and lifetimes is thoroughly examined with changes in the type of organic ligand.
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Andersson, David. "From the Electronic Structure of Point Defects to Functional Properties of Metals and Ceramics". Doctoral thesis, Stockholm : Materialvetenskap, Materials Science and Engineering, KTH, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4309.
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Zamani, Reza. "Structure nanoengineering of functional nanomaterials. Advanced electron microscopy study". Doctoral thesis, Universitat de Barcelona, 2013. http://hdl.handle.net/10803/145318.
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In this report novel materials for advanced applications are studied by means of the latest microscopy technologies and methodologies which have had a dramatic impact on progress of materials science. The aim was to study phenomena such as polytypism, unusual morphologies, polytypic branching, cation ordering, polarity, epitaxial growth and interface, etc, in order to find adequate explanations for the influence of the phenomena on the properties and applications such as thermoelectricity, p-n junction functionality, photovoltaic efficiency, optoelectronic properties, and sensing response. Various semiconducting materials, i.e. complex chalcogenides, metal oxides, and III-V nanostructures were characterized for this purpose. Here, nanoengineered structures of functional materials at nanoscale are studied by means of advanced electron microscopy methods.
Chapter 1 gives a brief introduction to the report; the main purpose of the work, state-of-the-art, challenges and possibilities. In chapter 2 the methodology is described. The results are provided in Chapter 3, 4, and 5, and Chapter 6 is the general conclusions and the outlook. Note that Chapters 3-5 have their own introduction and conclusion. Therefore, chapter 1 consists of a short introduction to the general idea of the study, its importance and the state-of-the-art, and a preface of the thesis.
In Chapter 2, after a brief history and the basic concepts of EM, the TEM methodology is described; the advanced TEM techniques used to study the nanostructured semiconductors at atomic scale. In general, it consists of brief descriptions of basic principles of TEM techniques. As experimental results are corroborated by theoretical studies and simulations, these procedures (image processing, simulations, etc) are also described shortly.
Chapter 3 is dedicated to nanoengineering crystal structure and morphology of nanocrystals of complex copper-based chalcogenide, from binaries to complex ternaries and quaternaries. In this chapter it is shown that there is a wide range of possibilities for engineering, as many elements can be substituted with the primary cations and anions. Advanced TEM studies are performed in order to figure out the physics behind the property modifications. Phenomena such as morphology change, polytypism, ordering, polarity, electronic band change, strain, etc are elaborately studied, and correlated to the physical properties such as thermoelectricity.
CCTSe polypods are the case of a complete structure study to understand the branching mechanism. Therefore, by means of an aberration-corrected TEM the polarity and cation ordering was determined. Polarity-driven morphology and branching mechanism is explained. Moreover, electronic band structure in this polytypic structure is simulated.
Chapter 4 is based on the study of nanojunctions in metal oxide heterostructured NWs, structures that can enhance the functionality of the targeted devices, such as photovoltaic cells, or gas sensors. Production of nanojunctions is a successful approach in the context. In this chapter it is shown how coaxial heterostructuring of NWs, e.g. formation of core-shell structures increase the efficiency of the solar cells or enhance the sensitivity/selectivity of the gas sensors.
In chapter 5 almost the same approach was followed, nevertheless, this time with III-V NWs. The importance of axial heterostructures and fully-epitaxial and relaxed structure are emphasized. The optoelectronic properties of the GaN NWs, such promising p-n junctions, are examined. Polarity issue, as a remarkably influencing parameter, is precisely studied experimentally. Its effect on electronic band structure in the heterointerface is also proven by the theoretical simulations.
In the end, a general conclusion of the whole work and room for further study and future work is discussed in Chapter 6. The ample freedom of structural nanoengineering in the materials, together with development of novel electron microscopy techniques, opens the way towards the new possibilities for the future work.En este trabajo hemos estudiado materiales avanzados con las últimas tecnologías y metodologías de microscopía electrónica, las que tienen un impacto importante en el desarrollo de la ciencia de materiales. El objetivo principal ha sido estudiar fenómenos como el politipismo, morfologías inusuales, ramificación, ‘ramificación politípica’, manipulación de la estructura de banda, ordenación de los cationes, polaridad, crecimiento e interfase epitaxial, alojamiento de una fase secundaria en una base, etc. para razonar la influencia de aquellos fenómenos en las propiedades y aplicaciones, por ejemplo la termoelectricidad, el funcionamiento de unión p-n, la eficiencia de las celdas solares, las propiedades optoelectrónicas, la respuesta de los sensores, etc. Distintos semiconductores han sido caracterizados: nanopartículas de calcogenuros complejos, nanohilos de óxidos de metales, y nanohilos del grupo III-V. Hemos estudiado los materiales en escala nanométrica por medio de métodos avanzados de microscopía electrónica de transmisión (TEM). El capítulo 1 es una breve introducción a la tesis, en la que se exponen los objetivos principales del trabajo, los últimos avances (state-of-the-art), los retos, y las nuevas posibilidades. En el capítulo 2 se explica la metodología de TEM utilizada para estudiar los semiconductores. Los capítulos 3 a 5 se componen de los resultados. El capítulo 3 está basado en el análisis de las nanopartículas de calcogenuros complejos. La sección de resultados contiene tres partes: monoestructurados, multiestructurados, y heteroestructuradas de tipo core-shell. En caso de nanopartículas cuaternarias de CCTSe, las nanopartículas ramifican y forman polipodes, que es el caso de un estudio elaborado porque el mecanismo de la ramificación es interesante. En capítulo 4 se trabaja con los nanohilos de óxidos de metales que sirven para muchas aplicaciones como celdas solares o sensores de gas. En nuestro caso, con el objetivo de mejorar la funcionalidad de los aparatos, hemos estudiado heteroestructuras. En el capítulo 5 prácticamente la misma aproximación está escogida, pero esta vez con nanohilos del grupo III-V. Aquí hemos enfatizado la importancia del crecimiento epitaxial de heteroestructuras. Por último, en el capítulo 6 hemos hablado de las conclusiones generales y las perspectivas para la investigación futura.
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Chen, Rongzhen. "First-Principles Study on Electronic and Optical Properties of Copper-Based Chalcogenide Photovoltaic Materials". Doctoral thesis, KTH, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-207626.
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To accelerate environmentally friendly thin film photovoltaic (PV) technologies, copper-based chalcogenides are attractive as absorber materials. Chalcopyrite copper indium gallium selenide (CIGS ≡ CuIn1–xGaxSe2) is today a commercially important PV material, and it is also in many aspects a very interesting material from a scientific point of view. Copper zinc tin sulfide selenide (CZTSSe ≡ Cu2ZnSn(S1–xSex)4) is considered as an emerging alternative thin film absorber material. Ternary Cu2SnS3 (CTS) is a potential absorber material, thus its related alloys Cu2Sn1–xGexS3 (CTGS) and Cu2Sn1–xSixS3 (CTSS) are attractive due to the tunable band gap energies. CuSb(Se1–xTex)2 and CuBi(S1–xSex)2 can be potential as ultra-thin (≤ 100 nm) film absorber materials in the future. In the thesis, analyses of these Cu-based chalcogenides are based on first-principles calculations performed by means of the projector augmented wave method and the full-potential linearized augmented plane wave formalisms within the density functional theory as implemented in the VASP and WIEN2k program packages, respectively. The electronic and optical properties of CIGS (x = 0, 0.5, and 1) are studied, where the lowest conduction band (CB) and the three uppermost valence bands (VBs) are parameterized and analyzed in detail. The parameterization demonstrates that the corresponding energy dispersions of the topmost VBs are strongly anisotropic and non-parabolic even very close to the Γ-point. Moreover, the density-of-states and constant energy surfaces are calculated utilizing the parameterization, and the Fermi energy level and the carrier concentration are modeled for p-type CIGS. We conclude that the parameterization is more accurate than the commonly used parabolic approximation. The calculated dielectric function of CuIn0.5Ga0.5Se2 is also compared with measured dielectric function of CuIn0.7Ga0.3Se2 collaborating with experimentalists. We found that the overall shapes of the calculated and measured dielectric function spectra are in good agreement. The transitions in the Brillouin zone edge from the topmost and the second topmost VBs to the lowest CB are responsible for the main absorption peaks. However, also the energetically lower VBs contribute significantly to the high absorption coefficient. CTS and its related alloys are explored and investigated. For a perfectly crystalline CTS, reported experimental double absorption onset in dielectric function is for the first time confirmed by our calculations. We also found that the band gap energies of CTGS and CTSS vary almost linearly with composition over the entire range of x. Moreover, those alloys have comparable absorption coefficients with CZTSSe. Cu2XSnS4 (X = Be, Mg, Ca, Mn, Fe, Ni, and Zn) are also studied, revealing rather similar crystalline, electronic, and optical properties. Despite difficulties to avoid high concentration of anti-site pairs disordering in all compounds, the concentration is reduced in Cu2BeSnS4 partly due to larger relaxation effects. CuSb(Se1–xTex)2 and CuBi(S1–xSex)2 are suggested as alternative ultra-thin film absorber materials. Their maximum efficiencies considering the Auger effect are ~25% even when the thicknesses of the materials are between 50 and 300 nm.QC 20170523
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Wang, Haihang. "PAOFLOW-Aided Computational Materials Design". Thesis, University of North Texas, 2019. https://digital.library.unt.edu/ark:/67531/metadc1609102/.
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Functional materials are essential to human welfare and to provide foundations for emerging industries. As an alternative route to experimental materials discovery, computational materials designs are playing an increasingly significant role in the whole discovery process. In this work, we use an in-house developed python utility: PAOFLOW, which generates finite basis Hamiltonians from the projection of first principles plane-wave pseudopotential wavefunctions on pseudo atomic orbitals(PAO) for post-process calculation on various properties such as the band structures, density of states, complex dielectric constants, diffusive and anomalous spin and charge transport coefficients. In particular, we calculated the dielectric function of Sr-, Pb-, and Bi-substituted BaSnO3 over wide concentration ranges. Together with some high-throughput experimental study, our result indicates the importance of considering the mixed-valence nature and clustering effects upon substitution of BaSnO3 with Pb and Bi. We also studied two prototype ferroelectric rashba semiconductors, GeTe and SnTe, and found the spin Hall conductivity(SHC) can be large either in ferroelectric or paraelectric structure phase. Upon doping, the polar displacements in GeTe can be sustained up to a critical hole concentration while the tiny distortions in SnTe vanish at a minimal level of doping. Moreover, we investigated the sensitivity of two dimensional group-IV monochalcogenides to external strain and doping, which reveal for the first time giant intrinsic SHC in these materials, providing a new route for the design of highly tunable spintronics devices based on two-dimensional materials.
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Almutairi, Alanoud. "Electronic band structure equations and Fermi surface evolution from 2D materials to 3D layered superconducting compounds". Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/134414/1/Alanoud%20Mulfi%20Z_Almutairi_Thesis.pdf.
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A simple approach for extracting the superconducting gap of materials from trendline fittings of key sections of their Electronic Band Structures (EBS), calculated using Density Functional Theory (DFT), is presented. The proposed approach works well for very different compositions, structure types and superconducting transition temperatures, indicating that it is robust, reliable and versatile. This approach provides many advantages in terms of required computational time and power, compared with similar information extracted from phonon dispersion calculations, making it accessible to wider DFT-computational chemistry and physics communities. The approach also identifies requirements for superconductivity and indirectly contributes towards understanding of superconductivity mechanisms.
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Shimogawa, Hiroyuki. "Development of Functional Organic Materials with an Intramolecular B-N Coordination Bond as a Key Scaffold". 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225619.
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Souza, de Almeida Jailton. "Designing and Tuning the Properties of Materials by Quantum Mechanical Calculations". Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6923.
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Murillo, Navarro Diana Elisa. "Electronic structure calculations of defects in diamond for quantum computing : A study of the addition of dopants in the diamond structure". Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-74268.
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When doing computations on the negatively (positively) charged NV-center in diamond, the common procedure is to add (subtract) an electron from the system. However, when using periodic boundary conditions, this addition/subtraction of an electron from the supercell would result in a divergent electrostatic energy. So an artificial background jellium charge of opposite charge that compensate the electronic charge to make the supercell neutral is needed. This introduces further problems that needs corrections. And this method is especially problematic for slab supercells, as the compensating background charge leads to a dipole, which diverges as the vacuum between the slab images increases. An alternative, recently proposed way of charging the NV-center is to introduce electron donors/acceptors in the form of nitrogen/boron atoms (at substitutional sites in the diamond lattice). In this way, we keep the supercell/slab neutral, and avoid correction schemes. In this work we verify that the addition of a substitutional nitrogen atom indeed has the same effect on the NV-center as the more traditional method of adding an extra electron to the system. Further, we investigate the effects of 1. Adding two substitutional nitrogen atoms to the system (3 nitrogen atoms in total, neutral supercell), 2. Adding a substitutional nitrogen atom and an electron to the system (2 nitrogen atom in total, negatively charged supercell), 3. Adding two electrons to the system (1 nitrogen atom, doubly negatively charged supercell). Additionally, we investigate the addition of acceptor dopants (boron) in order to analyze the effect on the electronic structure of the NV-center and diamond.
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Ball, Molly R. "First Principles Study of Electronic and Magnetic Structures in Double Perovskites". The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1483702986122186.
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Deitz, Julia. "Bridging the Gap: Probing Structure-Property Relationships in Functional Materials through Advanced Electron Microscopy Based Characterization". The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1543506730719345.
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Constantinescu, Gabriel Cristian. "Large-scale density functional theory study of van-der-Waals heterostructures". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274876.
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Research on two-dimensional (2D) materials currently occupies a sizeable fraction of the materials science community, which has led to the development of a comprehensive body of knowledge on such layered structures. However, the goal of this thesis is to deepen the understanding of the comparatively unknown heterostructures composed of different stacked layers. First, we utilise linear-scaling density functional theory (LS-DFT) to simulate intricate interfaces between the most promising layered materials, such as transition metal dichalcogenides (TMDC) or black phosphorus (BP) and hexagonal boron nitride (hBN). We show that hBN can protect BP from external influences, while also preventing the band-gap reduction in BP stacks, and enabling the use of BP heterostructures as tunnelling field effect transistors. Moreover, our simulations of the electronic structure of TMDC interfaces have reproduced photoemission spectroscopy observations, and have also provided an explanation for the coexistence of commensurate and incommensurate phases within the same crystal. Secondly, we have developed new functionality to be used in the future study of 2D heterostructures, in the form of a linear-response phonon formalism for LS-DFT. As part of its implementation, we have solved multiple implementation and theoretical issues through the use of novel algorithms.
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Mullen, Ashley Lynn. "A Polarizable and Transferable Carbon Dioxide Potential for Materials Simulation". Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4832.
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Intermolecular potential energy functions for CO2 have been developed from first principles for use in heterogeneous systems, including one with explicit polarization. The intermolecular potentials have been expressed in a transferable form and parameterized from nearly exact electronic structure calculations. Models with and without explicit many-body polarization effects, known to be important in simulation of interfacial processes, are constructed. The models have been validated on pressure-density isotherms of bulk CO2 and adsorption in three metal-organic framework (MOF) materials. The present models appear to offer advantages over high quality fluid/liquid state potentials in describing CO2 interactions in interfacial environments where sorbates adopt orientations not commonly explored in bulk fluids. Thus, the nonpolar CO2-PHAST and polarizable CO2-PHAST* potentials are recommended for materials/interfacial simulations.
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Wolak, Matthaeus Anton. "The Electronic Structure of Biomolecular Self-Assembled Monolayers". Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4258.
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The studies presented here address the characterization of the electronic structure of various self-assembled monolayers (SAMs) of peptide nucleic acid (PNA) and tetraphenylporphyrin (TPP) SAMs and arrays, formed on gold substrates.
PNA is a promising alternative to DNA for bio-sensing applications, as well as for strategies for self-assembly based on nucleic acid hybridization. In recent years charge transfer through PNA molecules was a focus of research due to possible applications in self-assembled molecular circuits and molecular tools. In light of this research it is interesting to investigate the electronic structure of PNA interfaces to gold, a potential electrode material.
TPP is, due to its electronic structure, an organic p-type molecular semiconductor. Such a material can provide an alternative to standard micro- and optoelectronic devices and in recent years more attention was paid to semiconducting polymers and organic compounds offering these low-cost and flexible alternatives. Therefore, it is of high importance to investigate the prospect of using modified TPP molecules for the formation of interconnected molecular networks on metallic surfaces.
All investigated monolayers were formed from solution in a nitrogen atmosphere inside a homemade glove box. This process allowed for PNA SAM and TPP SAM and array formation on clean Au substrates without the exposure to the ambient atmosphere. Ultraviolet and X-ray photoemission spectroscopy (UPS and XPS) measurements on the resulting PNA SAMs and TPP SAMs and arrays, which were performed in a to the glove box attached vacuum chamber containing a photoemission spectrometer, revealed the hole injection barriers at the interfaces and the interface dipoles.
In addition to the UPS and XPS measurements on PNA, electronic structure calculations based on molecular dynamics sampling of the PNA structure were obtained, yielding the HOMO-LUMO gap and the electronic density of states for PNA. Combined with the UPS data, the theoretical calculations enabled estimation of the charge injection barriers for the PNA SAMs at the interface, as well as the assignment of individual UP-spectral features to specific molecular orbitals.
The orbital line-up at the interface between the Au substrate and the PNA indicated a significant interface dipole resulting in the alignment of the Au Fermi level near the center of the PNA HOMO-LUMO gap. This alignment causes large charge injection barriers for both holes and electrons, and thus impedes charge transfer from Au into the PNA SAM. The study of PNA molecules with ferrocene termini showed that this hole injection barrier is shifted to lower energies at the PNA/ferrocene interface. This shift was explained with a molecular orbital reconfiguration through the presence of the ferrocene terminus. The further investigation of the dependence of the electronic structure of PNA SAMs, based on their orientation, showed that incomplete films containing flat lying molecules can have a significant impact on the charge injection barriers. The close proximity of the nucleobases to the Au surface offers new ways for charge transfer between the substrate and the PNA molecule through its nitrogen sites, leading to a lowering of the hole injection barrier at the interface.
The TPP arrays were formed by depositing AgNO3 on the Au substrate prior to TPP incubation using the electrospray technique. The interaction of AgNO3 with the TPP promoted the formation of an interconnected thin film forming a network on the Au substrate. The line-up at the Au/TPP interface without AgNO3 exposure showed an interface dipole formation with injection barriers that would potentially obstruct charge injection into the molecule. However, the addition of AgNO3 to the process resulted in the formation of fine structures, and lead to a lower hole injection barrier due to an induced dipole, which would ultimately improve charge transfer between the substrate and the thin film. A separate thiolated TPP derivative was used to form SAMs on a gold substrate. The SAM exhibited an even lower injection barrier than the mentioned TPP thin film with AgNO3 exposure, leading to the conclusion that a mix of both TPP derivatives could potentially lead to a SAM with long range interconnectivity and a low hole injection barrier towards the substrate.
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Råsander, Mikael. "A Theoretical Perspective on the Chemical Bonding and Structure of Transition Metal Carbides and Multilayers". Doctoral thesis, Uppsala universitet, Materialteori, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-123485.
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The present thesis deals with a theoretical description of issues regarding chemical bonding, structure and stability of transition metal carbides and multilayered structures. First principles density functional theory has been used extensively to investigate the properties of alloyed solutions of transition metal carbides. Joint theoretical and experimental investigations have shown that there is a driving force for carbon to be released from these ternary carbide systems as a response to the alloying. This release of carbon was shown to yield favorable lubricating properties in the case of alloyed solutions of Ti-Al-C, that were not present in the case of pure TiC, a property that can be used to design new materials that combine high hardness with favorable tribological properties. From calculations of the activation energy of C diffusion in the vicinity of substitutional transition metal impurities (M) in TiC, it is found that the mobility of C atoms is increased due to the presence of the impurities. The lowering of the activation energy barriers suggests that the mobility of C in alloyed solutions of Ti-M-C is increased and will be more pronounced at lower temperature than for C diffusion in TiC. The magnetic properties of alloyed solutions of Ti-Fe-C has been investigated using both theory and experiment. Theoretical calculations reveal that the magnetic moment and the critical temperature increase when increasing the Fe content as well as when lowering the C content in the system. Furthermore, the magnetic exchange parameters between Fe atoms were found to clearly reflect changes in the chemical bonding when varying the C content. Experimentally the magnetic properties were found to be rather substantial. Furthermore, the magnetic properties changes upon annealing due to the formation of Fe-rich and Fe-poor regions in the system. After long enough annealing times precipitates of α-Fe are formed which is consistent with theoretical predictions. The interaction between TiC(111) surfaces and C in the form of graphite has also been investigated. For these systems it was found that graphite was rather strongly bonded to the carbide surface and that the atomic as well as electronic structure at the interface depend on the termination of the carbide surface. This research was motivated by the recent interest in graphene, but also to investigate how carbide grains interacts with C when dispersed in a carbon matrix. A model for the calculation of structural parameters in multilayer structures has been presented and evaluated. The model is based on classical elasticity theory and uses the elastic constants of the materials constituting the multilayer as the only input.
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Matta, Sri Kasi Venkata Nageswara Rao. "Computational exploration of two-dimensional (2D) materials for solar energy applications". Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/134244/1/Sri%20Kasi%20Venkata%20Nageswara%20Rao%20Matta%20Thesis_Redacted.pdf.
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This project is to find innovative and alternate Nano-sized materials for solar energy applications. This include conversion of solar light energy into electricity or generate clean environment friendly fuels by breaking water into Oxygen and Hydrogen. The study has explored material characteristics at electronic level to reveal new properties. These revelations then compared amongst some of the organic and inorganic materials for the intended purpose. Innovative design of new carbon-compounds (termed as carbon Quantum dots) included in the study for use in the new generation Perovskite solar cells for charge transfer.
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Huang, Bowen. "Computational materials discovery : prediction of carbon dioxide and nitrogen-based compounds under pressure using density functional theory and evolutionary algorithm". Thesis, Poitiers, 2017. http://www.theses.fr/2017POIT2301/document.
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La découverte de nouveaux composés cristallins par simulation numérique est un défi majeur en Science des Matériaux. Aussi, trois familles sont à l'étude : les composés constitués de lithium et de dioxyde de carbone ; les phases nitrures MxNy avec M = Mg, Ba, Mo et Zr ; les systèmes GaPO4 et SiS2. Les structures cristallographiques sont déterminées in silico à l'aide de l'algorithme évolutionnaire USPEX couplé à des calculs DFT (VASP). L'étude du polymorphisme en fonction de la pression est conduite tandis que l'analyse des propriétés structurales et électroniques constitue le cœur de cette thèse. Nos travaux mettent clairement en évidence l'effet de la pression dans l'émergence de stoichiométries inhabituelles telles que Li2(CO2), MgN4, et BaN10. Certains de ces matériaux hypothétiques restent stables à pression atmosphérique. Il est montré que l'ajout d'un élément du bloc s autorise la « polymérisation » des molécules insaturées CO2 et N2 à des pressions plus basses. Ainsi, l'oxalate C2O42- polymérise en chaine infinie poly-dioxane à 33 GPa dans LiCO2 ; la nouvelle composition Li2CO2 présente des motifs de type éthène (-O)2C=C(O-)2 ; des chaînons N2, N3 et N4, des anions pentazolates N5- et des cycles N6 sont identifiés dans les phases AexNy, ainsi que des chaines covalentes infinies (1D) stabilisés par les cations alcalino-terreux Ae ; le composé Ba3N2 est un électride conducteur à pression ambiante et un isolant au-dessus de 5 GPa ; la structure stable de MoN2 a des entités N2 encapsulées, et non l'arrangement en feuillet de type MoS2 proposé par des expérimentateurs ; nos prédictions couplées aux données DRX permettent l'élucidation de la structure de GaPO4 à 20 GPaThe discovery of novel crystalline compounds by numerical simulation is a major challenge in Materials Science. Also, three families are being studied: compounds consisting of lithium and carbon dioxide; the MxNy nitride phases with M = Mg, Ba, Mo and Zr; the GaPO4 and SiS2 systems. The crystallographic structures are determined in silico using the evolutionary algorithm USPEX coupled with DFT calculations (VASP). The study of polymorphism as a function of pressure is carried out whereas the analysis of structural and electronic properties constitutes the heart of this thesis. Our work clearly presents the effect of pressure on the emergence of unexpected stoichiometries, such as Li2(CO2), MgN4, and BaN10. Some of these hypothetical materials remain stable at atmospheric pressure. It's shown that the addition of the s-block element allows the "polymerization" of the unsaturated molecules CO2 and N2 to be carried out at lower pressures. Thus, oxalate C2O42- polymerizes in an infinite poly-dioxane chain in LiCO2 at 33 GPa; the new Li2CO2 composition presents the ethene like (-O)2C=C(O-)2 motif; N2, N3 and N4 finite chains, N5-pentazolate anions, and N6 rings are identified in the AexNy phases, as well as, infinite covalent (1D) chains stabilized by the alkaline earth cations (Ae); the Ba3N2 compound is a conductive electride at ambient pressure and an insulator above 5 GPa; the ground stable structure of MoN2 has encapsulated N2 units, and is not the MoS2 type arrangement proposed by experimentalists; our predictions coupled with the XRD data allow the elucidation of the GaPO4 structure at 20 GPa
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Woods, Matthew. "Relativistic theory of photoemission for magnetic materials". Thesis, Keele University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325858.
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Wahiduzzaman, Mohammad [Verfasser], Thomas [Akademischer Betreuer] Heine, Ulrich [Akademischer Betreuer] Kleinekathöfer i Thorsten [Akademischer Betreuer] Klüner. "Parametrization in Computational Materials Science: Force Fields for Physisorption and Density-Functional-based Tight-Binding Method for Electronic Structure / Mohammad Wahiduzzaman. Betreuer: Thomas Heine. Gutachter: Thomas Heine ; Ulrich Kleinekathöfer ; Thorsten Klüner". Bremen : IRC-Library, Information Resource Center der Jacobs University Bremen, 2014. http://d-nb.info/1087315530/34.
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Griffith, Kent Joseph. "Atomic and electronic structure of complex metal oxides during electrochemical reaction with lithium". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/271191.
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Lithium-ion batteries have transformed energy storage and technological applications. They stand poised to convert transportation from combustion to electric engines. The discharge/charge rate is a key parameter that determines battery power output and recharge time; typically, operation is on the timescale of hours but reducing this would improve existing applications and open up new possibilities. Conventionally, the rate at which a battery can operate has been improved by synthetic strategies to decrease the solid-state diffusion length of lithium ions by decreasing particle sizes down to the nanoscale. In this work, a different approach is taken toward next-generation high-power and fast charging lithium-ion battery electrode materials. The phenomenon of high-rate charge storage without nanostructuring is discovered in niobium oxide and the mechanism is explained in the context of the structure–property relationships of Nb2O5. Three polymorphs, T-Nb2O5, B-Nb2O5, and H-Nb2O5, take bronze-like, rutile-like, and crystallographic shear structures, respectively. The bronze and crystallographic shear compounds, with unique electrochemical properties, can be described as ordered, anion-deficient nonstoichiometric defect structures derived from ReO3. The lessons learned in niobia serve as a platform to identify other compounds with related structural motifs that apparently facilitate high-rate lithium insertion and extraction. This leads to the synthesis, characterisation, and electrochemical evaluation of the even more complicated composition–structure–property relationships in ternary TiO2–Nb2O5 and Nb2O5–WO3 phases. Advanced structural characterisation including multinuclear solid-state nuclear magnetic resonance spectroscopy, density functional theory, X-ray absorption spectroscopy, operando high-rate X-ray diffraction, and neutron diffraction is conducted throughout to understand the evolution of local and long-range atomic structure and changes in electronic states.
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Zhang, Teng. "Synchrotron radiation study of free and adsorbed organic molecules". Licentiate thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-307787.
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In this licentiate thesis, organic molecules, namely Cobalt Phthalocyanine (CoPc) and Biphenylene, have been studied by means of synchrotron radiation-based spectroscopic methods (Photoemission Spectroscopy (PES) and X-ray Absorption Spectroscopy (XAS) in combination with Density Functional Theory (DFT) calculations. Paper I is a combined experimental and theoretical investigation of electronic structure of CoPc. addressing the atomic character of the Highest Occupied Molecular Orbital (HOMO) and the electronic configuration of the molecular ground state. Both these aspects are still under discussion since different experimental and theoretical studies have given controversial results. Previous works have indicated the CoPc ground state to either be described by the 2A1g or 2Eg, or by a mix of the two electronic configurations. Regrading the debated the atomic character of the HOMO of CoPc, it has been suggested to be either metal 3d-like and localized on the central Co atom or originating in the organic ligand of the molecule. In this thesis the valence photoemission results for CoPc in gas phase and as adsorbed films on Au(111) together with the DFT simulations, consistently indicate that the HOMO is derived only by the organic ligand, with mainly contribution from the carbon atoms with no metal character. Moreover, the good agreement between the experimental and theoretical results, confirms that the ground state of CoPc is correctly described by the 2A1g configuration. In Paper II, PES and XAS have been used to investigate the occupied and empty density of states of biphenylene films of different thicknesses, deposited onto a Cu(111) crystal. The results have been compared to previous gas phase spectra and single molecule Density Functional Theory (DFT) calculations to get insights into the possible modification of the molecular electronic structure in the film induced by the adsorption on a surface. Furthermore, XAS measurements allowed the characterizion of the variation of the molecular arrangement with the film thickness and helped to clarify the substrate-molecule interaction.
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Ortiz, Carlos. "First Principles Calculations of Electron Transport and Structural Damage by Intense Irradiation". Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-102376.
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Abboud, Ali. "Prédiction et simulation numérique de nouveaux matériaux à deux dimensions". Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0145.
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Dans le domaine des nanosciences, la recherche sur les matériaux possédant des dimensions réduites a connu des progrès spectaculaires. Tandis que de nombreux travaux ont été fait initialement sur le graphène, l'attention s'est ensuite portée vers d'autres matériaux bidimensionnels, tels que le nitrure de bore hexagonal ou encore les dichalcogénures de métaux de transition. Néanmoins, il est toujours nécessaire de trouver des matériaux possédant des caractéristiques équivalentes ou supérieures à celles des composés déjà connus. Dans le cadre de cette thèse, nous avons utilisé le calcul ab initio et plus particulièrement la théorie de la fonctionnelle de la densité pour prédire et comprendre les propriétés de trois familles de matériaux bidimensionnels. Premièrement, en prenant la structure du phosphorène comme structure de référence et en remplaçant le phosphore par des atomes voisins dans le tableau périodique, nous avons pu obtenir des matériaux inconnus jusqu'ici. Ensuite, nous nous sommes intéressés à des matériaux à base d'halogénures tels que AcOBr ou BaFCl, parmi d'autres. Enfin, nous avons mis l'accent sur des composés bidimensionnels quaternaires, tels que ScP2AgSe6, P2AgSe6Bi, P2CuBiSe6 et CuInP2 S6. Pour chaque matériau, nous avons démontré qu'il était dynamiquement stable et étudié sa structure électronique, et pour certains l'effet d'un champ électrique sur le matériau, ce qui ouvre la porte à de futures études expérimentales dans le domaineIn the field of nanosciences, research on materials with reduced dimensions has seen spectacular progress. While many works were initially done on graphene, the attention then came to other two-dimensional materials, such as hexagonal boron nitride or transition metal dichalcogenides. Nevertheless, it is still necessary to find materials with characteristics equivalent to or superior to those of the already known compounds. In this thesis, we used ab initio calculations and more particularly density functional theory to predict and understand the properties of three families of two-dimensional materials. First, taking the phosphorene structure as the reference and replacing phosphorus with neighboring atoms in the periodic table, we have been able to obtain unknown materials so far. Then we looked at halide materials such as AcOBr or BaFCl, among others. Finally, we have focused on two-dimensional quaternary compounds, such as ScP2AgSe6, P2AgSe6Bi, P2CuBiSe6 and CuInP2S6. For each compound, we demonstrated that it was dynamically stable and studied its electronic structure, and for some the effect of an electric field on the material, which opens the door for future experimental studies in the field
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Magné, Damien. "Synthèse et structure électronique de phases MAX et MXènes". Thesis, Poitiers, 2016. http://www.theses.fr/2016POIT2284/document.
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Les objectifs de ce travail sont d'une part d'étudier la structure électronique de carbures de titane bidimensionnels appartenant à la famille des MXènes, et d'autre part de synthétiser des films minces pour caractériser certaines de leurs propriétés. L'étude de la structure électronique a été réalisée sur le système Ti3C2T2 avec une attention particulière portée aux groupements de surface T (T=OH, F ou O) en comparant les résultats obtenus par spectroscopie de perte d'énergie des électrons à ceux des calculs ab initio. Cette étude, portée à la fois sur les excitations du gaz d'électrons de valence et des électrons de coeur, a permis de mettre en évidence la localisation des groupements de surface, ainsi que leur influence sur la structure électronique du MXene. La comparaison des simulations et des spectres expérimentaux a également permis de caractériser la nature chimique des groupements de surface. Enfin, la limite d'une telle étude est discutée en considérant les phénomènes d'irradiation responsables de la perte d'atomes d'hydrogène. La synthèse d'échantillons modèles nécessite la synthèse préalable d'un film mince de phase MAX précurseur pour le MXene : nous avons choisi la phase Ti2AlC, précurseur de Ti2C. La synthèse de Ti2AlC a été réalisée par recuit ex-situ de systèmes multicouches déposés à température ambiante. Les films ont été caractérisés par diffraction des rayons X et microscopie électronique en transmission. Au-delà de l'obtention d'un film mince de Ti2AlC texturé, cette étude a permis de montrer que la phase recherchée était obtenue via des mécanismes d'interdiffusions induisant la formation d'une solution solide métastable vers 400°C qui se transforme en phase MAX vers 600°C. Enfin, l'application de ce procédé à la phase V2AlC a permis de montrer l'importance de l'orientation de la phase initiale pour l'obtention d'un film mince texturéThe aim of this work is at first to study the electronic structure of bidimensional titanium carbide systems, belonging to the MXene family and also to synthesize thin films of such new materials to characterize their properties. The study of the electronic structure has been performed for the Ti3C2T2 MXene with a special attention to the T surface groups by using a combination of electron energy loss spectroscopy and ab initio calculations. This study, focused on both valence and core electrons excitations, enabled the identification of the surface group localization, their influence on the MXene electronic structure as well as their chemical nature. The limits of our TEM-based study is also discussed in view of irradiation phenomena which induce the loss of hydrogen atoms. The synthesis of a MXene thin film requires, beforehand, that of a MAX phase thin film: we opted for Ti2AlC, the precursor for the Ti2C MXene. The MAX phase thin film synthesis was carried out by ex-situ annealing of a multilayer layers. X-ray diffraction experiments and cross-sectional transmission electron microscopy observations show that a highly textured Ti2AlC thin film is obtained above 600°C after the formation, at 400°C, of a metastable solid solution. Finally, by using the same process for V2AlC, we demonstrate that the initial phase orientation plays a key role for the texture of the thin film so obtained
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Ford, Michael E. "Atomistic modelling of iron with magnetic analytic Bond-Order Potentials". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:c824a315-4038-4777-8487-08358cb9f569.
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The development of interatomic potentials for magnetic transition metals, and particularly for iron, is difficult, yet it is also necessary for large-scale atomistic simulations of industrially important iron and steel alloys. The magnetism of iron is especially important as it is responsible for many of the element's unique physical properties -- its bcc ground state structure, its high-temperature phase transitions, and the mobility of its self-interstitial atom (SIA) defects. Yet an accurate description of itinerant magnetism within a real-space formalism is particularly challenging and existing interatomic potentials based on the Embedded Atom Method are suited only for studies of near-equilibrium ferritic iron, due to their restricted functional forms. For this work, the magnetic analytic Bond-Order Potential (BOP) method has been implemented in full to test the convergence properties in both collinear and non-collinear magnetic iron. The known problems with negative densities of states (DOS) are addressed by assessing various possible definitions for the bandwidth and by including the damping factors adapted from the Kernel Polynomial Method. A 9-moment approximation is found to be sufficient to reproduce the major structural energy differences observed in Density Functional Theory (DFT) and Tight Binding (TB) reference calculations, as well as the volume dependence of the atomic magnetic moments. The Bain path connecting bcc and fcc structures and the formation energy of mono- and divacancies are also described well at this level of approximation. Other quantities such as the high-spin/low-spin transition in fcc iron, the bcc elastic constants and the SIA formation energies converge more slowly towards the TB reference data. The theory of non-collinear magnetism within analytic BOP is extended as required for a practical implementation. The spin-rotational behaviour of the energy is shown to converge more slowly than the collinear bulk energy differences, and there are specific problems at low angles of rotation where the magnitude of the magnetic moment depends sensitively on the detailed structure of the local DOS. Issues of charge transfer in relation to magnetic defects are discussed, as well as inadequacies in the underlying d-electron TB model.
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Arapan, Sergiu. "Understanding Physical Reality via Virtual Experiments". Doctoral thesis, Uppsala universitet, Institutionen för fysik och materialvetenskap, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9314.
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In this thesis I have studied some problems of condensed matter at high pressures and temperatures by means of numerical simulations based on Density Functional Theory (DFT). The stability of MgCO3 and CaCO3 carbonates at the Earth's mantle conditions may play an important role in the global carbon cycle through the subduction of the oceanic crust. By performing ab initio electronic structure calculations, we observed a new high-pressure phase transition within the Pmcn structure of CaCO3. This transformation is characterized by the change of the sp-hybridization state of carbon atom and indicates a change to a new crystal-chemical regime. By performing ab initio Molecular Dynamics simulations we show the new phase to be stable at 250 GPa and 1000K. Thus, the formation of sp3 hybridized bonds in carbonates can explain the stability of MaCO3 and CaCO3 at pressures corresponding to the Earth's lower mantle conditions. We have also calculated phase transition sequence in CaCO3, SrCO3 and BaCO3, and have found that, despite the fact that these carbonates are isostructural and undergo the same type of aragonite to post-aragonite transition, their phase transformation sequences are different at high pressures. The continuous improvement of the high-pressure technique led to the discovery of new composite structures at high pressures and complex phases of many elements in the periodic table have been determined as composite host-guest incommensurate structures. We propose a procedure to accurately describe the structural parameters of an incommensurate phase using ab initio methods by approximating it with a set of analogous commensurate supercells and exploiting the fact that the total energy of the system is a function of structural parameters. By applying this method to the Sc-II phase, we have determined the incommensurate ratio, lattice parameters and Wyckoff positions of Sc-II in excellent agreement with the available experimental data. Moreover, we predict the occurrence of an incommensurate high-pressure phase in Ca from first-principle calculations within this approach. The implementation of DFT in modern electronic structure calculation methods proved to be very successful in predicting the physical properties of a solid at low temperature. One can rigorously describe the thermodynamics of a crystal via the collective excitation of the ionic lattice, and the ab initio calculations give an accurate phonon spectra in the quasi-harmonic approximation. Recently an elegant method to calculate phonon spectra at finite temperature in a self-consistent way by using first principles methods has been developed. Within the framework of self-consistent ab initio lattice dynamics approach (SCAILD) it is possible to reproduce the observed stable phonon spectra of high-temperature bcc phase of Ti, Zr and Hf with a good accuracy. We show that this method gives also a good description of the thermodynamics of hcp and bcc phases of Ti, Zr and Hf at high temperatures, and we provide a procedure for the correct estimation of the hcp to bcc phase transition temperature.
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Wagner, Christian Friedemann. "Mechanical, Electronic and Optical Properties of Strained Carbon Nanotubes". Doctoral thesis, Universitätsbibliothek Chemnitz, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-226260.
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This dissertation deals with the calculation of the mechanical properties, electronic structure, electronic transport, and optical properties of strained carbon nanotubes (CNTs). CNTs are discussed for straintronics as their electronic bands show a strong strain-sensitivity. Further, CNTs are stiff, possess a large rupture strain and they are chemically inert, which make them a suitable material in terms of reliability and functionality for straintronic devices. Therefore, this work aims to explore the potential of strain-dependent CNT devices with regard to their mechanical, electronic, and optical properties from a first-principles point of view. There is no work so far that systematically compares these strain-dependent, physical properties from ab initio calculations, which are suitable for small CNTs only, to tight-binding calculations, which are suitable to model large CNTs. First, the structural and mechanical properties of CNTs are investigated: Structural properties are obtained by geometry optimization of many CNTs using density functional theory (DFT). The mechanical properties of CNTs are calculated in the same way. The resulting stress-strain relations are investigated and their key parameters are systematically displayed with respect to the CNT chirality and radius. The ground state electronic properties are calculated using tight-binding models and DFT. Both methods are compared systematically and it is explored where the tight-binding approximation can be applied in order to obtain meaningful results. On top of the electronic structure, a transport model is used to calculate the current through strained CNTs. The model includes the effect of ballistic conductance, parametrized electron-phonon scattering and the influence of an applied gate voltage. Finally, a computationally efficient model is described, which is able to predict the current through strained CNT transistors and enables to find optimal operation regimes for single-chirality devices and devices containing CNT mixtures. Optical properties of strained CNTs are explored by calculating quasiparticle excitations by the means of the GW approximation and the solution of the Bethe-Salpeter equation for CNT excitons. Due to the numerical effort of these approaches, the data for just one CNT is obtained. Still, it is explored how the above-mentioned many-body properties can be related to the ground state results for this CNT. This finally leads to empirical approaches that approximately describe the many-body results from the ground state properties. It is elucidated how such a model can be generalized to other CNTs in order to describe the strain dependence of their optical transitionsDiese Dissertation befasst sich mit der Berechnung der mechanischen Eigenschaften, der elektronischen Struktur, der Transport- und der optischen Eigenschaften von verspannten Kohlenstoffnanoröhrchen (engl. carbon nanotubes, CNTs). CNTs werden für die Straintronik diskutiert, da ihre elektronischen Bänder eine starke Dehnungsempfindlichkeit aufweisen. Weiterhin sind CNTs steif, besitzen eine hohe Zugfestigkeit und sind chemisch inert, weshalb sie in Bezug auf Zuverlässigkeit und Funktionalität ein geeignetes Material für straintronische Bauelemente sind. Ziel dieser Arbeit ist es daher, das Potenzial von dehnungsabhängigen CNT-Bauteilen hinsichtlich ihrer mechanischen, elektronischen und optischen Eigenschaften aus der Perspektive von first principles-Methoden zu untersuchen. Es gibt bisher keine Arbeit, in der die Ergebnisse verschiedener Methoden – ab initio-basierte Berechnungen für kleine CNTs und tight-binding Berechnungen, die näherungsweise die elektronische Struktur großer CNTs beschreiben – miteinander systematisch vergleicht. Einführend werden die strukturellen und mechanischen Eigenschaften von CNTs untersucht: Strukturelle Eigenschaften ergeben sich durch Geometrieoptimierung vieler CNTs mittels Dichtefunktionaltheorie (DFT). Die mechanischen Eigenschaften von CNTs werden in gleicher Weise berechnet. Die daraus resultierenden Spannungs-Dehnungs-Beziehungen werden untersucht und deren relevante Parameter systematisch in Abhängigkeit von CNT-Chiralität und CNT-Radius dargestellt. Die Eigenschaften des CNT-Grundzustands werden unter Verwendung von tight-binding-Modellen und DFT berechnet. Beide Methoden werden systematisch verglichen und es wird untersucht, wo die tight-binding-Näherung angewendet werden kann, um aussagekräftige Ergebnisse zu erzielen. Basierend auf der elektronischen Struktur der CNTs wird ein Transportmodell aufgesetzt, durch das der Strom durch verspannte CNTs berechnet werden kann. Dieses Modell beinhaltet den Einfluss der ballistischen Leitfähigkeit, Elektron-Phonon-Streuung in parametrisierter Form und den Einfluss eines Gates. Damit wird ein numerisch effizientes Modell beschrieben, das in der Lage ist, den Strom durch verspannte CNT-Transistoren vorherzusagen. Auf dessen Basis wird es möglich, optimale Arbeitsbereiche für reine CNT-Bauelemente und Bauelemente mit CNT-Mischungen zu berechnen. Die optischen Eigenschaften verspannter CNTs werden durch die Berechnung von Quasiteilchenanregungen mittels der GW-Approximation und der Lösung der Bethe-Salpeter-Gleichung für CNT-Exzitonen untersucht. Aufgrund des numerischen Aufwandes dieser Ansätze werden diese Daten für nur ein CNT erhalten. Daran wird der Zusammenhang zwischen den oben genannten Vielteilchen-Eigenschaften und den Grundzustandseigenschaften für dieses CNT demonstriert. Daraus ergeben sich empirische Ansätze, die es gestatten, die Vielteilchen-Ergebnisse näherungsweise auf die elektronischen Grundzustandseigenschaften zurückzuführen. Es wird dargestellt, wie ein solches Modell für andere CNTs verallgemeinert werden kann, um die Verspannungsabhängigkeit ihrer optischen Übergänge zu beschreiben
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Zhou, Ruiping. "Structural And Electronic Properties of Two-Dimensional Silicene, Graphene, and Related Structures". Wright State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=wright1341867892.
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Miroshnichenko, O. (Olga). "Properties of binary oxides:a DFT study". Doctoral thesis, Oulun yliopisto, 2019. http://urn.fi/urn:isbn:9789526223018.
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Abstract Titanium dioxide nanoparticles are used in an enormous amount of applications. Their properties are different from bulk TiO₂ and are affected by adsorbates that are unavoidably present on the surface. In this thesis, the effect of OH and SO₄ groups (the adsorbants present on the surface during manufacturing) on the properties of anatase-structured TiO₂ nanoparticles is studied. It was found that the above mentioned groups change both the geometric and electronic structure of nanoparticles, resulting in changes in the photoabsorption spectrum. Bader charges are calculated using electron density from Density Functional Theory calculations. They can be used for determination of the oxidation state of the atom. The relation between computed partial charges and oxidation states for binary oxides using data from open materials database has been demonstrated in this work using a linear regression. The applicability of the oxidation state determination by Bader charges for mixed valence compounds and surfaces is consideredTiivistelmä Titaanidioksidinanopartikkeleita käytetään lukuisissa sovelluksissa. Niiden ominaisuudet poikkeavat kiinteän TiO₂:n ominaisuuksista, ja niihin vaikuttavat pinnalle väistämättä absorboituvat aineet. Tässä työssä on tutkittu OH- ja SO₄-ryhmien vaikutusta anataasirakenteisten TiO₂-nanopartikkelien ominaisuuksiin. Tällaisia ryhmiä esiintyy yleisesti nanopartikkelien pinnalla valmistusprosessien aikana. Työssä havaittiin, että nämä ryhmät muuttavat nanopartikkelien rakenteellisia ja sähköisiä ominaisuuksia, ja siten vaikuttavat myös fotoabsorptiospektriin. Baderin varaukset voidaan laskea käyttäen tiheysfunktionaaliteoriaan perustuvista laskuista saatavaa elektronitiheyttä. Niitä voidaan käyttää atomin hapetustilan laskemiseen. Tässä työssä on osoitettu, että binääristen oksidien tapauksessa laskettujen osittaisvarauksien ja hapetustilan välillä on yhteys. Tämä yhteys voitiin osoittaa käyttämällä lineaarista regressiota. Työssä tarkastellaan myös menetelmän soveltuvuutta hapetustilojen määrittämiseen sekavalenssiyhdisteille ja pinnoille
Original papers Original publications are not included in the electronic version of the dissertation. Miroshnichenko O., Auvinen S., & Alatalo M. (2015). A DFT study of the effect of OH groups on the optical, electronic, and structural properties of TiO₂ nanoparticles. Phys. Chem. Chem. Phys., 17, 5321–5327. https://doi.org/10.1039/c4cp02789b Miroshnichenko O., Posysaev S., & Alatalo M. (2016). A DFT study of the effect of SO4 groups on the properties of TiO₂ nanoparticles. Phys. Chem. Chem. Phys., 18, 33068–33076. https://doi.org/10.1039/c6cp05681d http://jultika.oulu.fi/Record/nbnfi-fe201707037608 Posysaev S., Miroshnichenko O., Alatalo M., Le D., & Rahman T.S. (2019). Oxidation states of binary oxides from data analytics of the electronic structure. Comput. Mater. Sci., 161, 403–414. https://doi.org/10.1016/j.commatsci.2019.01.046
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Velez-Herrera, Pedro. "Functional Polybenzoxazine Resin as Advanced Electronic Materials". Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1201274106.
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Bush, Ian J. "The electronic structure of disordered materials". Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334224.
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Gardner, Paul William. "Electronic structure and prediction of materials". Thesis, University of Liverpool, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.570231.
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In this thesis the electronic structure and prediction of materials will be investi- gated, In the first two results chapters we will look at the use of Density Functional Theory primarily to investigate the Electronic Structure of materials, but also as a basic prediction tool, Ruddelesden-Popper layered structures ofthe form An+lBn03n+l (A=Ca, B=Mn) are investigated with emphasis placed on the geometry and reasons behind the formation methods required, GGA and GGA+U functionals are used to describe the n = 1 - 6 and n = 00 phases individually and to determine any trends in the size of the lattice, binding energies and geometries, There are energetic similarities as we increase n highlighting the need for alternative formation methods (Pulsed Laser Deposition) to conventional methods to prevent mixed phase structures as has been observed, The effect of doping or of restricting the size of a lattice with a substrate helps to reduce distortion in perovskite layers, enabling the formation of higher n-layered calcium manganese based Ruddlesden-Popper structures, M(L-cysteinate) structures can be formed (M=Cd,Zn), which feature one-dimensional substructures that can be viewed as fragments of bulk structures of CdS (rocksalt high pressure phase) and ZnS (wurtzite}. Considering the structural similarities with bulk materials, the optical properties of M(L-cysteinate) were studied and indicate blue shifts of the band gap with respect to the bulk MS structures, due to the low dimensionality of the metal-sulphur arrangement. Density of states calculations show strong electronic structure similarities with the bulk phases and rationalize the band gap changes, A comparison of Hybrid (HSE03) functionals and DFT (GGA) is made when evaluating the density of states. A Darwinian based evolutionary process called Genetic Algorithms is used to predict the ground state energy of clusters containing two model ion types of size N=4-20,30 with further insight for N=40,50. More primitive approaches to the selection and mating of clusters is used to simplify the GA process with successful comparison of results to previous work. A dependence on the number of clusters in the population evaluated is observed as we increase the number of ions in a cluster.
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Fedorov, Alexander. "Electronic structure of doped 2D materials". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-203500.
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Electronic systems are an indivisible part of modern life. Every day, new materials, devices, passive components, antennas for wireless communication are needed to be designed and developed. In particular, flexible and biocompatible wearable devices are urgent required for medical and industrial applications. The great hope lies in the materials with high crystalline quality and flexibility such as graphene and other 2D semiconductors and insulators. Doping is a conventional tool for tailoring of the electronic properties of the functional materials.
Here we examine application of the widely used the electron donor species to the graphene and hexagonal boron nitride monolayer (h-BN). For each we determine surface-interface properties and the full electronic band structure using the combination of the surface science methods such as angle-integrated and angle resolved photoemission (XPS, ARPES), electron diffraction (LEED) and photo absorption (XAS).
As the result we provided insight into mechanisms underlying the doping gating of the graphene h-BN monolayer by the alkali metals. We fully characterized their surface and interface structure. Finally we studied the interplay between electrons and phonons in the doped graphene and we demonstrated that Ca-doped graphene is the promising candidate for realizing superconductivity in graphene.
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Young, Callum A. "Local structure/property relationships in functional materials". Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:8eea6d96-5a48-4ed9-adad-e2b1fdc97acb.
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It is increasingly being realised that localised deviations from the average structure can play an important role in a material's properties, and hence an understanding of these deviations is essential when constructing a coherent picture of a system. In this thesis, both neutron and X-ray total scattering data have been collected and used to reveal information on three canonical systems: the high-temperature superconductor YBa2Cu3O7-x; the parent compound of the colossal magnetoresistive manganites, LaMnO3; and the oldest known magnetic material, Fe3O4. Reverse Monte Carlo refinements-using the RMCProfile implementation of the algorithm-have been used as the principal analysis technique, and the functionality of the RMCProfile program has been extended to allow the refinement of magnetic systems involving substitutional disorder. For YBa2Cu3O7-x, the focus of this thesis is on the apical Cu{O bond length. This is shown to have a bimodal distribution, but correlations in the displacements of both atoms disguise this fact in the average structure, thus resolving the apparent controversy that had existed between local- and average-structure probes. LaMnO3 displays (what was thought to be) a simple order{disorder transition that results in the Jahn-Teller distortion becoming invisible in the average structure above ~ 750 K. Here it is shown that in fact the transition is more complicated, and involves a change in the symmetry of the Jahn-Teller distortion, whereby the long Mn-O bonds move from being opposite one another in the octahedra to being adjacent to one another. This new distortion still breaks the degeneracy of the system, and is consistent with a wide range of existing observations. Finally the low temperature structure of Fe3O4 is examined using the updated RMCProfile code. The refinements show sensitivity to local structure variations, producing a bimodal Fe atom bond valence distribution. In addition, the refined magnetic spin configuration is presented, providing the first detailed description of the low-temperature magnetic structure. It is found to be a canted ferrimagnet, and appears to be consistent with Cc symmetry.