A química computacional apresenta a grande vantagem de prover informações fundamentais para espécies moleculares propostas, antes mesmo de sua síntese em laboratório. A Teoria do Funcional da Densidade é bastante utilizada nesta área, produzindo resultados satisfatórios para um grande número de propriedades e sistemas, mas com uma menor demanda por recursos computacionais que métodos mais avançados. Entretanto, o desenvolvimento de funcionais que incluem efeitos relativísticos ainda se encontra num estágio inicial. Em geral, tais efeitos são importantes em compostos de átomos pesados, embora devam ser considerados também em sistemas com átomos mais leves se a propriedade em estudo for particularmente sensível, como é o caso do gradiente de campo elétrico na posição de núcleos em moléculas. Assim, na primeira etapa desta dissertação foi avaliado o desempenho de funcionais comuns de troca-correlação não relativísticos, quando utilizados em conjunto com o formalismo de quatro componentes (tratamento relativístico), no estudo dos gradientes de campo elétrico em núcleos de átomos (índio, antimônio, iodo, lutécio e háfnio) constituindo moléculas diatômicas. Foram investigados funcionais baseados nas aproximações da densidade local e do gradiente generalizado, funcionais híbridos e que incluem correções em termos da atenuação com a distância. Nossos resultados, que estão em acordo com observações da literatura, ressaltam o melhor desempenho de funcionais híbridos e com correções de atenuação para esta propriedade e demonstram a importância do uso do método indireto. Posteriormente, foi feita uma nova parametrização de alguns dos melhores funcionais não relativísticos selecionados na etapa anterior (B3LYP, PBE0 e CAM-B3LYP), dentro do formalismo de quatro componentes, para uso no cálculo destes mesmos gradientes num grupo teste de átomos (cobre, iodo, lantânio e ouro) em moléculas lineares. Nestes casos, os funcionais modificados propostos tiveram um bom desempenho geral e foram particularmente bem sucedidos para cobre e ouro. Finalmente, é possível destacar o funcional híbrido PBE0 e sua modificação, proposta neste estudo, por conta de seu desempenho excelente, tanto para os metais como para os demais elementos que tiveram seus EFGs investigados aqui. / The computational chemistry has the great advantage of providing fundamental information for proposed molecular species even before their synthesis in laboratory. The Density Functional Theory is widely used in this area, producing satisfactory results for a large number of properties and systems, but with a lower demand for computational resources than that of more advanced methods. However, the development of functionals that include relativistic effects is still at an early stage. In general, these effects are important in compounds containing heavy elements, but they must also be considered in systems of lighter atoms if the studied property was particularly sensitive, as occurs for the electric field gradient at the position of nuclei in molecules. Thus, the first step of this dissertation was to evaluate the performance of common non-relativistic exchange-correlation functionals when used in conjunction with the four component formalism (relativistic treatment) in the study of electric field gradients at the nuclei of atoms (indium, antimony, iodine, lutetium and hafnium) forming diatomic molecules. Functionals based on the local density approximation and generalized gradient approximation, hybrid functionals and the ones that include attenuation corrections were investigated. Our results, which are in agreement with observations in the literature, highlight the best performance of hybrid functionals and attenuation corrections for this property and demonstrate the importance of using the indirect approach. Subsequently, there was a new parameterization of some of the best non-relativistic functionals selected in the previous step (B3LYP, PBE0 and CAM - B3LYP) within the four component formalism for calculations of these same gradients in a trial group of atoms (copper, iodine, lanthanum and gold) into linear molecules. In these cases, the modified functionals proposed had a satisfactory overall performance and were particularly successful for copper and gold. Finally, it is possible to mention the excellent performance of the hybrid functional PBE0 and its modification proposed in this study for both metals and the other elements that had their EFGs investigated here.

Les carbures et oxydes des métaux de transition sont d'une importance capitale dans le domaine industriel voir catalytique. Le carbure de tungstène WC a été identifié comme un bon substituant des métaux nobles tel que le platine dans le domaine catalytique. Le but de ce travail de thèse est d'appliquer des méthodes de chimie quantique les plus poussées pour déterminer la structure électronique, la stabilité et la nature de liaison chimique des diatomiques WC et WC2+. Notre recherche préliminaire est motivée par les données spectroscopiques disponibles sur W, W+, W2+, WC et WC2+. La méthodologie adoptée, CASSCF/MRCI/MRCI+Q/aug-cc-pV5Z(-PP) implémentée dans le code MOLPRO, consiste à réaliser des calculs quantique tenant en compte des effets de corrélation et relativistes avec un traitement spécifique du couplage spin−orbite pour la recherche des courbes d'énergie potentielle de l'état fondamental et des états excités de plus basses énergies de WCn+ (n=0-2) tout en utilisant une base suffisamment étendue. Les résultats de ce travail sont en bon accord avec ceux disponibles dans la littérature. En outre, dans ce travail nous avons confirmé pour la première fois que le carbure diatomique dicationique WC2+ est thermodynamiquement stable / Metal carbides and oxides are more interesting in catalytic and industrial domains. Tungsten carbide WC has been detected as serious substituent of platinum Pt catalytic. The ultimate goal of this thesis is theoretical studies of electronic structure, stability and the bound nature on WC, WO and its cations. Our preliminary research were motiving by the available spectroscopic data on W, W+, W2+, WC et WC2+. We used the methodology (CASSCF/MRCI/MRCI+Q/aug-cc-pV5Z(-PP)) implemented on MOLPRO package to perform quantum calculations with high accuracy taking into account the correlation and relativistic effects with a specific treatment of spin orbit coupling for some low lying excited electronic states of WCn+, (n=0, 1 et 2). Our results are shown in good agreement with those available in the literature. Furthermore, in this work for the first time we demonstrated that a carbide dication (WC2+) is thermodynamically stable

A química computacional apresenta a grande vantagem de prover informações fundamentais para espécies moleculares propostas, antes mesmo de sua síntese em laboratório. A Teoria do Funcional da Densidade é bastante utilizada nesta área, produzindo resultados satisfatórios para um grande número de propriedades e sistemas, mas com uma menor demanda por recursos computacionais que métodos mais avançados. Entretanto, o desenvolvimento de funcionais que incluem efeitos relativísticos ainda se encontra num estágio inicial. Em geral, tais efeitos são importantes em compostos de átomos pesados, embora devam ser considerados também em sistemas com átomos mais leves se a propriedade em estudo for particularmente sensível, como é o caso do gradiente de campo elétrico na posição de núcleos em moléculas. Assim, na primeira etapa desta dissertação foi avaliado o desempenho de funcionais comuns de troca-correlação não relativísticos, quando utilizados em conjunto com o formalismo de quatro componentes (tratamento relativístico), no estudo dos gradientes de campo elétrico em núcleos de átomos (índio, antimônio, iodo, lutécio e háfnio) constituindo moléculas diatômicas. Foram investigados funcionais baseados nas aproximações da densidade local e do gradiente generalizado, funcionais híbridos e que incluem correções em termos da atenuação com a distância. Nossos resultados, que estão em acordo com observações da literatura, ressaltam o melhor desempenho de funcionais híbridos e com correções de atenuação para esta propriedade e demonstram a importância do uso do método indireto. Posteriormente, foi feita uma nova parametrização de alguns dos melhores funcionais não relativísticos selecionados na etapa anterior (B3LYP, PBE0 e CAM-B3LYP), dentro do formalismo de quatro componentes, para uso no cálculo destes mesmos gradientes num grupo teste de átomos (cobre, iodo, lantânio e ouro) em moléculas lineares. Nestes casos, os funcionais modificados propostos tiveram um bom desempenho geral e foram particularmente bem sucedidos para cobre e ouro. Finalmente, é possível destacar o funcional híbrido PBE0 e sua modificação, proposta neste estudo, por conta de seu desempenho excelente, tanto para os metais como para os demais elementos que tiveram seus EFGs investigados aqui. / The computational chemistry has the great advantage of providing fundamental information for proposed molecular species even before their synthesis in laboratory. The Density Functional Theory is widely used in this area, producing satisfactory results for a large number of properties and systems, but with a lower demand for computational resources than that of more advanced methods. However, the development of functionals that include relativistic effects is still at an early stage. In general, these effects are important in compounds containing heavy elements, but they must also be considered in systems of lighter atoms if the studied property was particularly sensitive, as occurs for the electric field gradient at the position of nuclei in molecules. Thus, the first step of this dissertation was to evaluate the performance of common non-relativistic exchange-correlation functionals when used in conjunction with the four component formalism (relativistic treatment) in the study of electric field gradients at the nuclei of atoms (indium, antimony, iodine, lutetium and hafnium) forming diatomic molecules. Functionals based on the local density approximation and generalized gradient approximation, hybrid functionals and the ones that include attenuation corrections were investigated. Our results, which are in agreement with observations in the literature, highlight the best performance of hybrid functionals and attenuation corrections for this property and demonstrate the importance of using the indirect approach. Subsequently, there was a new parameterization of some of the best non-relativistic functionals selected in the previous step (B3LYP, PBE0 and CAM - B3LYP) within the four component formalism for calculations of these same gradients in a trial group of atoms (copper, iodine, lanthanum and gold) into linear molecules. In these cases, the modified functionals proposed had a satisfactory overall performance and were particularly successful for copper and gold. Finally, it is possible to mention the excellent performance of the hybrid functional PBE0 and its modification proposed in this study for both metals and the other elements that had their EFGs investigated here.

Abstract In this thesis, the theory of static magnetic resonance spectral parameters of nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spectroscopy is investigated in terms of the molecular Breit-Pauli Hamiltonian, which is obtained from the relativistic Dirac equation via the Foldy-Wouthuysen transformation. A leading-order perturbational relativistic theory of NMR nuclear shielding and spin-spin coupling tensors, and ESR electronic g-tensor, is presented. In addition, the possibility of external magnetic-field dependency of NMR parameters is discussed. Various first-principles methods of electronic structure theory and the role of one-electron basis sets and their performance in magnetic resonance properties in terms of their completeness profiles are discussed. The presented leading-order perturbational relativistic theories of NMR nuclear shielding tensors and ESR electronic g-tensors, as well as the theory of the magnetic-field dependent NMR shielding and quadrupole coupling are evaluated using first-principles wave function and density-functional theories.

Cette thèse traite de l'application des approches topologiques de la liaison chimique à des systèmes contenant des éléments lourds sujets aux effets relativistes, notamment ceux dépendant du spin. Elle présente deux volets principaux : (i) l'évaluation des effets du couplage spin-orbite (SO) sur la structure électronique à l'aide d'une analyse combinée des propriétés de la fonction ELF et de l'approche QTAIM en deux composantes et (ii) la rationalisation des distorsions structurales pour des molécules impliquant des éléments lourds et le rôle du couplage SO dans ces distorsions. Nous avons pu mettre en évidence différentes situations pour lesquelles le couplage SO peut avoir une influence très importante, modérée ou négligeable. Un résultat important de ce travail démontre la dépendance du couplage SO à son environnement chimique. Pour le second volet, nous avons élaboré une approche qui a consisté à établir une corrélation entre les interactions électrostatiques locales entre régions liantes et non liantes (bassins ELF et QTAIM) et la géométrie moléculaire du système dans l'esprit des modèles VSEPR et du Ligand Close Packing (LCP). Cette approche a notamment mis en évidence la connexion entre la structure moléculaire et les répulsions des paires non-liantes de l'atome central avec leur environnement. / This thesis deals with the aplication of topological approaches of the chemical bonding by means of analysing properties of density-based functions like Electron Localization Function (ELF) and the Quantum Theory of Atoms in Molecumes (QTAIM) to systems involving heavy elements such as 6p elements or actinides . It is divided into two main parts: (i) the evaluation of the spin-orbit coupling (SOC) effects on the electronic structure by means of combination of the QTAIM and ELF topological analyses in the field of quasirelativistic quantum calculations, and (ii) the rationalization of structural distorsions on molecules containing heavy atoms, and the role of the SOC on these distorsions. We were able to emphasize different situations for which SOC has strong, moderate or tiny influence on the chemical bonding, depending on the chemical environnement on which the heavy element is involved. In the second part of this thesis we tested our approach consisting of ELF/QTAIM interbasin repulsion energy analysis in connection with the molecular geometry of the system, in the spirit of the VSEPR and LCP models.

During the past decades, the development of laser technology has produced pulses with increasingly higher peak intensities. These can now be made such that their strength rivals, and even exceeds, the atomic potential at the typical distance of an electron from the nucleus. To understand the induced dynamics, one can not rely on perturbative methods and must instead try to get as close to the full machinery of quantum mechanics as practically possible. With increasing field strength, many exotic interactions such as magnetic, relativistic and higher order electric effects may start to play a significant role. To keep a problem tractable, only those effects that play a non-negligible role should be accounted for. In order to do this, a clear notion of their relative importance as a function of the pulse properties is needed.  In this thesis I study the interaction between atomic hydrogen and super-intense laser pulses, with the specific aim to contribute to the knowledge of the relative importance of different effects. I solve the time-dependent Schrödinger and Dirac equations, and compare the results to reveal relativistic effects. High order electromagnetic multipole effects are accounted for by including spatial variation in the laser pulse. The interaction is first described using minimal coupling. The spatial part of the pulse is accounted for by a series expansion of the vector potential and convergence with respect to the number of expansion terms is carefully checked. A significantly higher demand on the spatial description is found in the relativistic case, and its origin is explained. As a response to this demanding convergence behavior, an alternative interaction form for the relativistic case has been developed and presented. As a guide mark for relativistic effects, I use the classical concept of quiver velocity, vquiv, which is the peak velocity of a free electron in the polarization direction of a monochromatic electromagnetic plane wave that interacts with the electron. Relativistic effects are expected when vquiv reaches a substantial fraction of the speed of light c, and in this thesis I consider cases up to vquiv=0.19c. For the present cases, relativistic effects are found to emerge around vquiv=0.16c .

Les carbures et oxydes des métaux de transition sont d'une importance capitale dans le domaine industriel voir catalytique. Le carbure de tungstène WC a été identifié comme un bon substituant des métaux nobles tel que le platine dans le domaine catalytique. Le but de ce travail de thèse est d'appliquer des méthodes de chimie quantique les plus poussées pour déterminer la structure électronique, la stabilité et la nature de liaison chimique des diatomiques WC et WC2+. Notre recherche préliminaire est motivée par les données spectroscopiques disponibles sur W, W+, W2+, WC et WC2+. La méthodologie adoptée, CASSCF/MRCI/MRCI+Q/aug-cc-pV5Z(-PP) implémentée dans le code MOLPRO, consiste à réaliser des calculs quantique tenant en compte des effets de corrélation et relativistes avec un traitement spécifique du couplage spin−orbite pour la recherche des courbes d'énergie potentielle de l'état fondamental et des états excités de plus basses énergies de WCn+ (n=0-2) tout en utilisant une base suffisamment étendue. Les résultats de ce travail sont en bon accord avec ceux disponibles dans la littérature. En outre, dans ce travail nous avons confirmé pour la première fois que le carbure diatomique dicationique WC2+ est thermodynamiquement stable / Metal carbides and oxides are more interesting in catalytic and industrial domains. Tungsten carbide WC has been detected as serious substituent of platinum Pt catalytic. The ultimate goal of this thesis is theoretical studies of electronic structure, stability and the bound nature on WC, WO and its cations. Our preliminary research were motiving by the available spectroscopic data on W, W+, W2+, WC et WC2+. We used the methodology (CASSCF/MRCI/MRCI+Q/aug-cc-pV5Z(-PP)) implemented on MOLPRO package to perform quantum calculations with high accuracy taking into account the correlation and relativistic effects with a specific treatment of spin orbit coupling for some low lying excited electronic states of WCn+, (n=0, 1 et 2). Our results are shown in good agreement with those available in the literature. Furthermore, in this work for the first time we demonstrated that a carbide dication (WC2+) is thermodynamically stable

Modern solid state chemistry is inconceivable without theoretical treatment of solids thanks to the availability of efficient and accurate computational methods. Being developed mainly by physicist's community and deeply rooted in the formalism of reciprocal space, they often lack connections to familiar chemical concepts, indispensable for the chemical understanding of matter. Quantum chemical topology approach is a powerful theory able to efficiently recover chemical entities from the abstract description of a system given by its density matrices. It can be used to partition any many-electron system into the atoms, using the topology of electron density or for instance into atomic shells, using the topology of ELI-D field. Various characteristics of interactions between these chemical building blocks can be obtained applying bonding indicators, e.g. from the analysis of domain-averaged properties. Quantum chemical topology methods have been extended in the current work for the applications on the diversity of theoretical methods widely used for the description of solids nowadays – from the mean field Kohn-Sham density functional theory to the reduced one-electron density matrices functional theory or from the scalar-relativistic methods to the many-component formalisms employing spinor wavefunctions. It has been shown, that they provide chemically meaningful description of the bonding which is universally applicable to any class of extended systems, be it ionic insulator, covalent solid or metal. It has been shown, that the relativistic effects on the chemical bonding can be easily revealed using extensions of bonding indicators developed in the current work. Classical chemical concepts like Zintl-Klemm concept can be easily recovered with these descriptions. Intimate connection between the class of the material and the degree of chemical bonding delocalization has been also established. All these methods have been successfully applied to the various classes of solids and delivered novel insights on their crystal structure, properties, solid state transitions and reactivity.

Modern solid state chemistry is inconceivable without theoretical treatment of solids thanks to the availability of efficient and accurate computational methods. Being developed mainly by physicist's community and deeply rooted in the formalism of reciprocal space, they often lack connections to familiar chemical concepts, indispensable for the chemical understanding of matter. Quantum chemical topology approach is a powerful theory able to efficiently recover chemical entities from the abstract description of a system given by its density matrices. It can be used to partition any many-electron system into the atoms, using the topology of electron density or for instance into atomic shells, using the topology of ELI-D field. Various characteristics of interactions between these chemical building blocks can be obtained applying bonding indicators, e.g. from the analysis of domain-averaged properties. Quantum chemical topology methods have been extended in the current work for the applications on the diversity of theoretical methods widely used for the description of solids nowadays – from the mean field Kohn-Sham density functional theory to the reduced one-electron density matrices functional theory or from the scalar-relativistic methods to the many-component formalisms employing spinor wavefunctions. It has been shown, that they provide chemically meaningful description of the bonding which is universally applicable to any class of extended systems, be it ionic insulator, covalent solid or metal. It has been shown, that the relativistic effects on the chemical bonding can be easily revealed using extensions of bonding indicators developed in the current work. Classical chemical concepts like Zintl-Klemm concept can be easily recovered with these descriptions. Intimate connection between the class of the material and the degree of chemical bonding delocalization has been also established. All these methods have been successfully applied to the various classes of solids and delivered novel insights on their crystal structure, properties, solid state transitions and reactivity.

No description available.