<p>Fullerenes have been shown to constitute a prototypical building block for truly nanometer-sized devices and exotic nanounit-based materials, e.g., high-temperature superconductors. This makes the detailed understanding of fullerene electronic states in compounds and at interfaces of primary importance, since the high symmetry of the molecule greatly </p><p>simplifies the starting point of the analysis. Carbon nanotubes, which combine one macroscopic with two nanoscopic dimensions, are perhaps of even greater practical interest.</p><p>Angle-dependent electron spectroscopies have been employed in the present work to study these materials, characterizing their structure, bonding, and electronic states. For solid C₆₀, the photoelectron angular distribution has been found to be essentially that of the free molecule, modified by solid state scattering; a similar distribution is found for K₃C_60.</p><p>The surface and bulk electronic structure of K₃C₆₀ has been identified by angle-dependent core and valence photoelectron spectroscopy (PES) and x-ray emission spectroscopy. An insulating surface layer has been identified for this high-temperature superconductor.</p><p>Angle-dependent valence PES is used to investigate the electronic states of C₆₀/Al(110). Electron correlations are found to be the origin of the splitting observed in the molecular orbitals, which is quite sensitive to the molecular orientation. The components of the highest occupied molecular orbital are differentiated according to their overlap with the substrate.</p><p>A rigid shift of valence- and core-levels has been observed even for ionic and covalent C₆₀compounds, reflecting the efficient static polarizability screening of the molecule. </p><p>The alignment of multi-walled carbon nanotubes has been investigated by x-ray absorption spectroscopy, using the spectral intensity ratio of π*- and *-resonances. Core level combined with valence PES shows that the degree of defect structure varies from position to position on the sample. Valence photoelectron spectra of defect-free sample spots closely resembles the total DOS of graphite.</p>

Fullerenes have been shown to constitute a prototypical building block for truly nanometer-sized devices and exotic nanounit-based materials, e.g., high-temperature superconductors. This makes the detailed understanding of fullerene electronic states in compounds and at interfaces of primary importance, since the high symmetry of the molecule greatly simplifies the starting point of the analysis. Carbon nanotubes, which combine one macroscopic with two nanoscopic dimensions, are perhaps of even greater practical interest. Angle-dependent electron spectroscopies have been employed in the present work to study these materials, characterizing their structure, bonding, and electronic states. For solid C60, the photoelectron angular distribution has been found to be essentially that of the free molecule, modified by solid state scattering; a similar distribution is found for K3C60. The surface and bulk electronic structure of K3C60 has been identified by angle-dependent core and valence photoelectron spectroscopy (PES) and x-ray emission spectroscopy. An insulating surface layer has been identified for this high-temperature superconductor. Angle-dependent valence PES is used to investigate the electronic states of C60/Al(110). Electron correlations are found to be the origin of the splitting observed in the molecular orbitals, which is quite sensitive to the molecular orientation. The components of the highest occupied molecular orbital are differentiated according to their overlap with the substrate. A rigid shift of valence- and core-levels has been observed even for ionic and covalent C60 compounds, reflecting the efficient static polarizability screening of the molecule. The alignment of multi-walled carbon nanotubes has been investigated by x-ray absorption spectroscopy, using the spectral intensity ratio of π*- and *-resonances. Core level combined with valence PES shows that the degree of defect structure varies from position to position on the sample. Valence photoelectron spectra of defect-free sample spots closely resembles the total DOS of graphite.

We describe the rare-earth elements using the Hubbard I approximation. We show that the theory reproduces the cohesive properties, like the volume and bulk modulus, and we find an excellent agreement between theory and experiment for the (inverse) photo emission spectra of the valence band. In addition we reproduce the spin and orbital moments of these elements. This licentiate thesis contains an introduction to the cohesive, magnetic and spectral properties of the rare-earth elements, to density functional theory and to density functional theory in combination with dynamical mean-field theory within the Hubbard I approximation. We also focus on some technical details, e.g. the optimal basis used in the electronic structure code and the role of charge self-consistency in properly describing the valence electrons.

Les recherches menées dans le cadre de cette thèse avaient un double objectif. Premièrement, le développement d’une nouvelle méthode de chimie quantique à croissance linéaire basée sur le concept d’Orbitales Moléculaires Extrêmement Localisées (ELMOs) et adaptée à l’étude de très gros systèmes moléculaires. Deuxièmement, il s’agit d’évaluer le potentiel des méthodes de calcul utilisant de fonctions d’ondes contraintes et leur capacité à reproduire des données de diffraction aux rayons-X. En ce qui concerne le premier objectif, notre approche se base sur le principe de transférabilité, à savoir l’observation que les systèmes moléculaires sont composés par des unités fonctionnelles récurrentes qui conservent leurs caractéristiques lorsqu’elles se trouvent dans un même environnement chimique. Malheureusement, les orbitales moléculaires traditionnellement employées en chimie théorique dans des modèles de particule indépendante (Hartree-Fock, Kohn-Sham) sont complètement délocalisées sur le système étudié et, par conséquent, ne peuvent pas être transférées d’une molécule à une autre. Ce problème peut être résolu en ayant recours à des orbitales moléculaires déterminées de manière variationnelle sous la contrainte d’être exprimées à partir des fonctions de base centrées sur des atomes de fragments présélectionnés : les ELMOs. En fait, puisqu’elles sont strictement localisées, ces orbitales sont en principe transférables d’une molécule à une autre. L’objectif à terme est d’exploiter cette transférabilité en construisant une base de données d’ELMOs permettant de calculer quasiment instantanément, de manière approximative, des fonctions d’ondes et des densités électroniques de macromolécules. Dans la première partie de cette thèse, nous avons évalué le degré de transférabilité des orbitales moléculaires extrêmement localisées et nous avons proposé une approximation appropriée pour les molécules modèles servant à la détermination des ELMOs qui seront stockées dans la future base de données. Nous avons également comparé la transférabilité des ELMOs avec celle de densités électroniques atomiques asphériques (pseudo-atomes) qui sont largement répandues en cristallographie pour le raffinement de structure cristallographique de grands systèmes. La seconde partie de la thèse se focalise sur les méthodes quantiques utilisant des fonctions d’ondes contraintes. Dans ces méthodes, on cherche à déterminer des fonctions d’ondes qui minimisent l’énergie électronique des systèmes étudiés, mais qui en même temps doivent reproduire un jeu d’amplitudes de facteurs de structure expérimentaux. Cette technique, initialement proposée par Jayatilaka, a récemment été étendue à la théorie des orbitales moléculaires extrêmement localisées. Dans ce contexte, nous avons tout d’abord étudié les effets d’une localisation stricte sur la structure électronique dans des calculs de la fonction d’onde contrainte. Puis, nous avons déterminé si la fonction d’onde contrainte (et la densité associée) est capable de capturer des effets de la corrélation électronique. Enfin, en utilisant une nouvelle technique dite Valence Bond "expérimentale", basée sur les ELMOs, nous avons effectué une étude théorique sur le syn-1,6:8,13- Biscarbonyl[14] annulène (BCA) pour expliquer la rupture partielle de son aromaticité à haute pression observée expérimentalement. Cette dernière étude illustre positivement la potentialité du concept d’orbitale moléculaire strictement localisée en chimie quantique, qui ouvre des perspectives très larges notamment pour l’étude statique ou dynamique de systèmes moléculaires complexes. / The goal of the present work was dual. At first, this thesis aimed at proposing new lin- ear scaling quantum chemistry methods based on Extremely Localized Molecular Orbitals (ELMOs) and, secondly, it focused on the assessment of the capabilities of the X-ray con- strained wave function approaches. Concerning the first target, our approach is based on the transferability principle, namely the observation that molecular systems are composed by recurrent functional units that generally keep their features when they are in a similar chemical environment. In this context, it is possible to take advantage of the intrinsic trans- ferability of molecular orbitals strictly localized on small molecular subunits to recover wave functions and electron densities of large systems. Unfortunately, the molecular or- bitals traditionally used in quantum chemistry are completely delocalized on the system in exam and, therefore, are not transferable from a molecule to another. This problem can be solved only considering molecular orbitals variationally determined under the constraint of expanding them on local basis sets associated with pre-determined molecular fragments: the ELMOs. In fact, since they are strictly localized, these orbitals are in principle transfer- able from molecule to molecule and our final goal is to construct databanks of ELMOs that will enable to recover almost instantaneously approximate wave functions and electron densities of macromolecules at a very low computational cost. In the first part of this the- sis, we have evaluated the transferability of the Extremely Localized Molecular Orbitals and we have defined a suitable model molecule approximation for the computation of the ELMOs to be stored in the future databases. We have also compared the transferability of the ELMOs to the one of the aspherical atomic electron densities (pseudoatoms), which are largely used in crystallography to refine crystallographic structures of large systems. The second part of this work focuses on the X-ray constrained wave function approach. This method consists in determining wave functions that not only minimize the electronic energy of the systems under exam, but that also reproduce sets of experimental structure factor amplitudes within a desired accuracy. The technique, initially proposed by Jayatilaka has been recently extended to the theory of the Extremely Localized Molecular Orbitals. In this context, we have first studied the effects of introducing a strict a priori localization on the electronic structure in X-ray constrained wave function calculations. Then, we have determined if the X-ray constrained wave function is intrinsically able to capture the elec- tron correlation effects on the electron densities. Finally, also exploiting a novel X-ray con- strained ELMO-based Valence Bond technique, we have reported theoretical studies on the syn-1,6:8,13-Biscarbonyl[14] annulene (BCA) to explain the partial rupture of the aromatic character of the molecule occurring at high-pressure

A natureza das ligações de hidrogênio e a influência destas interações na estrutura eletrônica de complexos neutros, catiônicos, aniônicos e radicalares foi estudada utilizando-se análises geométricas, energéticas, eletrônicas e topológicas. Inicialmente, verificaram-se alterações na aromaticidade do cátion pirílio após a complexação com uma a três moléculas de água. Tais complexos foram ainda estudados em meio reacional com constante dielétrica igual a da água com o emprego do modelo PCM (Polarizable Continuum Model). Adicionalmente, os efeitos da hidroxilação na estrutura eletrônica dos cátions benzopirílio e flavílio foram considerados. Posteriormente, analisaram-se os efeitos das fortes ligações de hidrogênio na ressonância do grupo carboxila em complexos formados entre o radical hidroperoxil e os ácidos fórmico, acético e trifluoroacético. Como extensão desse trabalho, estudos envolvendo complexos obtidos com e sem restrições na otimização de geometria possibilitaram obter informações a respeito da ressonância dos grupos carboxila e carboxilato quando o fluoreto de hidrogênio interage linear ou perpendicularmente com todos os átomos do ácido fórmico e do ânion formiato. O desenvolvimento das atividades supracitadas compreendeu a análise da função de onda pelos métodos NBO (Natural Bond Orbital), NSA (Natural Steric Analysis), NRT (Natural Resonance Theory) e AIM (Atoms in Molecules). As alterações em parâmetros geométricos e nas cargas atômicas foram consideradas. Uma análise energética foi realizada com o emprego do método de decomposição de energia proposto por Xantheas. As freqüências vibracionais e a intensidade das bandas do estiramento do grupo X-H, doador da ligação de hidrogênio, foram analisadas. As densidades de spin para os complexos radicalares também foram obtidas. A influência das ligações de hidrogênio e o efeito do substituinte na aromaticidade dos cátions foram verificados com o emprego dos métodos e índices NICS (Nucleus Independent Chemical Shifts), HOMA (Harmonic Oscillator Model of Aromaticity), HOSE (Harmonic Oscillator Stabilization Energy) e PDI (para-Delocalization Index). Os cálculos foram efetuados com os modelos B3LYP/6-31+G(d,p), B3LYP/6-311++G(3df,3pd) e UB3LYP/6-311++G(3df,3pd). Ocasionalmente, outras funções de base (EPR-III e cc-pVDZ), assim como o método MP2, foram utilizados para testar a confiabilidade dos resultados obtidos. As interações intermoleculares pouco alteraram a estrutura eletrônica e a aromaticidade do cátion pirílio. Analogamente, a substituição de um átomo de hidrogênio por um grupo hidroxila em diversas posições dos cátions benzopirílio e flavílio também não provocou modificações muito significativas na estrutura eletrônica desses cátions, embora tenha se verificado uma dependência da aromaticidade com a posição da hidroxila. Por outro lado, a distorção geométrica associada às ligações de hidrogênio foram responsáveis pelo incremento ou diminuição da ressonância do grupo carboxila nos ácidos fórmico, acético, trifluoroacético e do grupo carboxilato no ânion formiato. Os efeitos dos grupos doador e sacador de elétrons na estabilização dos complexos radicalares foram evidenciados. Adicionalmente, pode-se atribuir um caráter covalente parcial em algumas ligações de hidrogênio. / The nature of hydrogen bonds and their influence on electronic structure of neutral, cationic, anionic, and radical complexes was studied by using geometric, energetic, electronic, and topological analysis. The changes in aromaticity of the pyrylium cation upon complexation with one up to three water molecules were investigated. The PCM (Polarizable Continuum Model) model was employed to study the pyrylium-water complexes in a water reaction medium. In addition, the effects of hydroxylation on electronic structure of the benzopyrylium and flavilium cations were also considered. In addition, the effects of strong hydrogen bonds on carboxyl group resonance in the complexes formed between the hydroperoxyl radical and formic, acetic, and trifluoroacetic acids were analyzed. In extension of this work, studies including complexes, obtained with and without geometric restrictions, provided information about the resonance of the carboxyl and carboxylate groups when the hydrogen fluoride interacts, linear or perpendicularly, with all atoms of formic acid and formate anion. The analysis of the wavefunction by using NBO (Natural Bond Orbital), NSA (Natural Steric Analysis), NRT (Natural Resonance Theory), and AIM (Atoms in Molecules) methods was necessary to the development of the above mentioned activities. The changes in geometric parameters and atomic charges were also considered. An energetic analysis of complexes was done with the energy decomposition method proposed by Xantheas. The vibrational frequencies and the intensity of the X-H (hydrogen bond donor group) stretching bands were studied. The spin densities for the radical complexes were also obtained. The Nucleus Independent Chemical Shifts (NICS), Harmonic Oscillator Model of Aromaticity (HOMA), HOSE (Harmonic Oscillator Stabilization Energy), and PDI (para-Delocalization Index) aromaticity criteria were employed to verify the hydrogen bond influence and the effect of hydroxylation in the aromaticity of the cations. The calculations were carried out by using B3LYP/6-31+G(d,p), B3LYP/6-311++G(3df,3pd), and UB3LYP/6-311++G(3df,3pd) models. Occasionally, other basis set (EPR-III and cc-pVDZ), as well as the MP2 method, were applied to test the accuracy of the results. The intermolecular interactions lead to small alterations in the electronic structure and aromaticity of pyrylium cation. Similarly, the substitution at different positions of the benzopyrylium and flavilium cations by a hydroxyl group does not cause significant changes in the electronic structure of these cations. However, a dependence of the hydroxyl group position on aromaticity was observed. On the other hand, for formic, acetic, trifluoroacetic acids, as well as for the formate anion, the resonance of the carboxyl and carboxylate groups is affected not only by the geometric distortions but also by the hydrogen bonds. The effects of the electron-donating and electron-withdrawing groups in the stabilization of radical complexes were characterized. Furthermore, a partial covalent character can be attributed to some hydrogen bonds.

Neste trabalho foram estudados computacionalmente os [2.2]ciclofanos ([2.2]paraciclofano (1), anti-[2.2]metaciclofano (2a), sin-[2.2]metaciclofano (2b) e [2.2]metaparaciclofano (3)), que são os [2n]ciclofanos mais simples, contendo dois anéis fenílicos conectados por duas pontes etilênicas. Os ciclofanos têm apresentado inúmeras aplicações importantes, podendo atuar como auxiliares em sínteses assimétricas e como catalisadores que simulam funções enzimáticas, apresentando seletividade em relação aos substratos. Eles são empregados tanto em químicab supramolecular quanto em áreas biomédicas. Estudos que empregam ressonância de spin eletrônico ou que investigam propriedades ópticas não-lineares dos [2.2]ciclofanos indicam que os mesmos apresentam interações transanulares, que ocorrem através de recobrimento direto entre orbitais pertencentes a anéis diferentes, through-space, ou através de recobrimento entre orbitais dos anéis e das pontes, through-bond. As interações transanulares possuem um papel fundamental na química dos ciclofanos, alterando o comportamento reacional destes compostos e as transições espectroscópicas. Apesar dos métodos de preparação de ciclofanos, desde os mais simples aos mais complexos, serem intensamente investigados, estudos computacionais, que busquem compreender as correlações entre tensão e aromaticidade, estrutura eletrônica e o mecanismo de ocorrência das interações transanulares, são raramente encontrados na literatura. Desse modo, o objetivo deste trabalho foi estudar as interações transanulares, bem como correlacionar as diferenças estruturais, a tensão sobre anéis e pontes, cargas atômicas, aromaticidade e os deslocamentos químicos, não apenas para os isômeros dos [2.2]ciclofanos, mas também seus derivados fluorados (perfluoração de um dos anéis dos [2.2]ciclofanos), bem como avaliar os efeitos de diversos substituintes (CN, Cl, C=O, NH2 e NO2) e da protonação na estrutura eletrônica do isômero [2.2]paraciclofano. As otimizações de geometria de 1, realizadas com diferentes métodos e conjuntos de funções de base, mostraram que os modelos MP2/6-31+G(d,p) e B3PW91/6-31+G(d,p) fornecem os melhores resultados em comparação com os dados de raios-x. Buscas conformacionais mostraram que 2a e 2b são confôrmeros com energias diferentes e que 3 possui dois confôrmeros degenerados. As energias relativas e de tensão das pontes, seguiram a mesma ordem, indicando que a tensão sobre as pontes e a repulsão entre as nuvens ? dos anéis aromáticos são determinantes para a estabilidade dos [2.2]ciclofanos. As reações isodésmicas indicaram que os anéis comportam-se como absorvedores de tensão. NICS e HOMA mostraram que apesar das perdas de planaridade dos anéis a aromaticidade é mantida. O método NBO confirmou que todos os [2.2]ciclofanos apresentam interações through-bond, mas apenas 2a e 2b apresentaram interações through-space significantes. A análise AIM mostrou que as interações transanulares observadas são do tipo camada fechada (iônica ou ligação de hidrogênio) e que estabilizam os [2.2]ciclofanos. Para os derivados fluorados as principais alterações geométricas observadas foram para os diedros das pontes. As reações isodésmicas revelaram que as tensões das pontes e as energias relativas são afetadas pela fluoração. Além disso, os anéis dos isômeros fluorados absorvem mais tensão que os anéis dos isômeros não fluorados. NICS e HOMA mostraram que a substituição por flúor aumenta a aromaticidade dos [2.2]ciclofanos. A análise NBO indicou que a perfluoração aumentou o número e a intensidade das interações through-space, mas as mesmas ficaram restritas principalmente aos derivados fluorados de 2a e 2b. A mesma análise evidenciou que há uma conjugação dos pares de elétrons dos átomos de flúor com o sistema ?. Por outro lado, a análise AIM sugeriu que a substituição não aumenta o número de interações through-space, mas confirmou a conjugação dos pares de elétrons dos átomos de flúor. Os demais substituintes empregados afetam os parâmetros geométricos do [2.2]paraciclofano (1) de maneira diferenciada. A análise particionada das reações isodésmicas mostrou que as tensões nos anéis e nas pontes dependem não apenas do substituinte empregado, mas também da posição da substituição. NICS e HOMA indicaram que a aromaticidade no anel não-substituído dos derivados substituídos é maior que em 1. A análise NBO revelou que a substituição e a protonação aumentam a ocorrência de interações transanulares through-space. O método AIM indicou a presença de interações transanulares apenas para o derivado substituído com NH2 e CN e para a espécie protonada. No entanto, tais interações apresentaram características de interações de camada fechada. com pequenas estabilizações. As cargas atômicas e os deslocamentos químicos confirmaram as mudanças na densidade eletrônica, observadas através do método AIM. / In this work, the [2.2]cyclophanes ([2.2]paracyclophane (1), anti-[2.2]metacyclophane (2a), syn-[2.2]metacyclophane (2b) e [2.2]metaparacyclophane (3)), which are the simplest [2n] cyclophanes that contain two phenyl rings connected by two ethanediyl linkages, were studied computationally. Cyclophanes have presented several important applications, such as auxiliary in asymmetric synthesis, catalysts that simulate enzymatic functions, presenting selectivity in relation to the substrates. They are employed either in supramolecular chemistry or in biomedical areas. Studies that apply electron spin resonance or that investigate the non-linear optical properties of [2.2]cyclophanes, indicate that these compounds present transannular interactions, which occur through direct overlap of orbitals lying in different rings, throughspace, or through overlap between orbitals from rings and bridges, through-bond. The transannular interactions have a fundamental role in cyclophane chemistry, changing the reactional behavior of these compounds, and the spectroscopic transitions. Despite the fact that the well known methods of preparation, from the simplest to the most complex cyclophanes, have been studied intensively, computational studies that intent to comprehend the correlations between tension and aromaticity, electronic structure, and the mechanism of the transannular interactions are rarely found in the literature. Therefore, the aim of this work was not only to study the transannular interactions, correlating the structural differences, tension in rings and bridges, atomic charges, aromaticity, and chemical shifts of the [2.2]cyclophanes isomers but also to extent a similar treatment to the fluorinated derivatives. In addition, the effects of substituents such as (CN, Cl, C=O, NH2, and NO2) and the protonation on the electronic structure of [2.2]paracyclophane were also evaluated. The geometry optimizations of 1, carried out by using different methods and basis set, showed that the models MP2/6-31+G(d,p) and B3PW91/6-31+G(d,p) provide the best results in comparison with the x-ray data. Conformational searches showed that 2a and 2b are the conformers that present the same energy and the isomer 3 has two degenerated conformers. The strain energies of the bridges followed the same tendency as the relative energies, indicating that the tension on the bridges and the repulsions between the ? clouds of the aromatic rings are the key factors that determine the [2.2]cyclophane stabilities. The isodesmic reactions indicated that the rings are absorbents of tension. NICS and HOMA showed that the aromaticity of the rings is preserved despite the changes on the planarity. The NBO method confirmed that all [2.2]cyclophanes present through-bond interactions, but only 2a and 2b exhibit noteworthy through-space interactions. The AIM analysis pointed out that the transannular interactions behave as closed shell interactions (ionic or hydrogen bond), stabilizing the [2.2]cyclophanes. The main geometric changes, observed to the fluorinated derivatives, were those related with the dihedral angle of bridges. The isodesmic reactions pointed out that the tensions of bridges and the relative energies are affected by the fluorination. In addition, the fluorinated rings absorb more tension than the non-fluorinated rings. NICS and HOMA showed that the substitution by fluorine increases the aromaticity of the [2.2]cyclophanes. The NBO analysis indicated that the number of through-space interactions increase with the fluorination, but it is restrict to the derivatives of 2a and 2b. In addition, the same analysis pointed out a conjugation of the fluorine lone pairs with the ? system. On the other hand, the AIM analysis suggested that the substitution do not increase the number of through-space interactions, but confirmed the conjugation of the fluorine lone pairs. The other substituents can affect the geometric parameter of 1 noticeably. The partitioned analysis of isodesmic reactions showed that the tensions in bridges and rings not only depend on the substituents employed but also on the position of substitution. NICS and HOMA pointed out that the aromaticity is bigger in the non-substituted rings of [2.2]paracyclophane derivatives than in 1. The NBO analysis showed that the substitution and protonation increase the number of through-space interactions. AIM method indicated the transannular interactions occur only to the derivate substituted by NH2 and CN, and to the protonated specie. However, these interactions presented features of closed shell interactions with small stabilizations. The atomic charges and the chemical shifts confirmed the changes of the electronic density, observed through the AIM method.

Our thesis tackles the many-electronic problem considering a non-relativistic and a relativistic orbital approach. Using the suites of programs ATSP and GRASP, we are able to approximate many-electron wave functions beyond the independent particle model by considering a superposition of CSFs. The optimization process, based on the variational principle, provides the best possible mixing coefficients fixing the linear combination of CSFs and spin-orbital basis on which we impose the orthonormality condition between functions of the same l or kappa subspace. Using this conventional approach within the relativistic framework, we estimate different properties of the triply ionized antimony atom (Sb IV), namely transition energies, transition probabilities, isotope shifts and a hyperfine-induced transition.<p><p>In the aim of partially relaxing the orthogonality constraints between correlation orbitals, we use the variational principle for targeting specific correlation effects by tailoring the configuration space. Independent sets of correlation orbitals, embedded in PCF, are produced from MCHF calculations. These non-orthogonal functions span CSF spaces that are coupled to each other by solving the associated generalized eigenvalue problem. The Hamiltonian and overlap matrix elements are evaluated using the biorthonormal orbital transformations and the efficient counter-transformations of the configuration interaction eigenvectors. This original method is successfully applied for describing different light atomic systems such as Li I, Be I, B I, C II and Ne I. An unwanted effect, called the ``constraint effect', is described and studied for these particular atomic systems. Even if this constraint can be completely relaxed through the DPCFI method, the computational resources required by such an approach lead us to study some simple strategies relaxing partially this constraint. This study takes it place in the context of neutral beryllium for which we test two particular strategies: one based on a weight criterion and one based on the type of excitations. Before concluding, we expose some developments combining the SCF process and the biorthonormal condition to relax the orthogonality constraints that are presently applied to the optimization process of the spin-orbital basis.<p>/<p>Dans notre thèse, nous abordons le problème polyélectronique dans un contexte non-relativiste et relativiste en adoptant une approche orbitalaire. En utilisant les suites de programmes reconnues ATSP et GRASP, nous sommes aptes à approcher des fonctions d'ondes polyélectroniques au-delà du modèle des particules indépendantes en utilisant une superposition de CSFs. Le processus d'optimisation, basé sur le principe des variations, fournit la meilleure estimation possible des coefficients de mélange, fixant la combinaison linéaire de CSFs et la meilleure base de spin-orbitales sur laquelle on impose la condition d'orthonormalité entre les fonctions appartenant au même sous-espace l ou kappa. En adoptant cette approche dans un cadre relativiste, nous évaluons des énergies de transition, des probabilités de transition, des déplacements isotopiques ainsi qu'une transition induite par mélange hyperfin pour l'atome d'antimoine trois fois ionisé (Sb IV).<p><p>Dans le but de relâcher partiellement les contraintes d'orthogonalité entre les orbitales de corrélation, nous utilisons le principe des variations afin de cibler des effets précis de la corrélation en taillant l'espace des configurations. Les ensembles indépendants d'orbitales de corrélation sont obtenus via la méthode MCHF. Les espaces de CSFs, exprimés sur ces fonctions mono-électronique non-orthogonales, sont couplés en résolvant le problème aux valeurs propres généralisé associé. Les matrices Hamiltonienne et de recouvrement sont déterminées au moyen de la technique des transformations biorthonormales et de la contre-transformation des vecteurs propres associés. Cette méthode originale est utilisée avec succès pour décrire des systèmes atomiques légers comme Li I, Be I, B I, C II et Ne I. Un effet indésirable, appelé ``effet de contrainte', est déecrit et étudié pour ces derniers systèmes atomiques. Même si ces contraintes peuvent-être en principe totalement levées au travers de la méthode DPCFI, les ressources nécessaires à l'application de cette dernière approche nous ont conduit à la recherche de stratégies simples et efficaces autorisant leur levée partielle. Pour ce faire, dans le cadre de nos calculs réalisés sur l'atome de béryllium, nous avons envisagé deux stratégies particulières: l'une basée sur les coefficients de mélange et l'autre basée sur le type d'excitation. Avant de conclure, nous proposons quelques développements combinant le processus auto-cohérent et la condition de biorthonormalité dans le but de relâcher les contraintes d'orthogonalité appliquées lors du processus d'optimisation de la base de spin-orbitales. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

The development of the correlation consistent basis sets, cc-pVnZ (where n = D, T, Q, etc.) have allowed for the systematic elucidation of the intrinsic accuracy of ab initio quantum chemical methods. In density functional theory (DFT), where the cc-pVnZ basis sets are not necessarily optimal in their current form, the elucidation of the intrinsic accuracy of DFT methods cannot always be accomplished. This dissertation outlines investigations into the basis set requirements for DFT and how the intrinsic accuracy of DFT methods may be determined with a prescription involving recontraction of the cc-pVnZ basis sets for specific density functionals. Next, the development and benchmarks of a set of cc-pVnZ basis sets designed for the s-block atoms lithium, beryllium, sodium, and magnesium are presented. Computed atomic and molecular properties agree well with reliable experimental data, demonstrating the accuracy of these new s-block basis sets. In addition to the development of cc-pVnZ basis sets, the development of a new, efficient formulism of the correlation consistent Composite Approach (ccCA) using the resolution of the identity (RI) approximation is employed. The new formulism, denoted 'RI-ccCA,' has marked efficiency in terms of computational time and storage, compared with the ccCA formulism, without the introduction of significant error. Finally, this dissertation reports three separate investigations of the properties of FOOF-like, germanium arsenide, and silicon hydride/halide molecules using high accuracy ab initio methods and the cc-pVnZ basis sets.

Diese Arbeit beschäftigt sich mit den besonderen elektronischen Eigenschaften der Übergangsmetall-Aluminide. In Anlehnung an die Quasikristalle und ihre Approximanten zeigt sich, dass selbst Materialien mit kleinen Einheitszellen die gleichen überraschenden Effekte aufweisen. So gibt es unter den Übergangsmetall-Aluminiden auch semimetallische und halbleitende Verbindungen, auch wenn sie aus klassisch-metallischen Komponenten wie Fe, Al oder Cr bestehen. Diese Eigenschaften sind außerdem mit einem tiefen Pseudogap bzw. Gap in der Zustandsdichte und starken kovalenten Bindungen gekoppelt. Bindungen werden im Rahmen dieser Arbeit durch zwei wesentliche Eigenschaften beschrieben. Erstens durch die Bindungsladung und zweitens durch die energetische Auswirkung der Bindung. Es ergibt sich, dass im Fall halbleitender Übergangsmetall-Aluminide zum einen eine Sättigung von bestimmten Bindungen, wie auch ein bindungs-antibindungs-Wechsel bei der Fermi-Energie vorliegt. Mit der Analyse der Nahordnung in Form der sogenannten lokalen Koordinationspolyeder ist es gelungen, eine einfache Regel für Halbleiter aufzustellen, die Fünffachkoordination für Al. Diese Regel besagt, dass Aluminium-Atome mit ihren drei Valenzelektronen nicht in der Lage sind, mehr als fünf gesättigte Bindungen zu ihren nächsten Übergangsmetall-Nachbarn aufzubauen. In exzellenter Übereinstimmung mit den in Annahme gleichartiger Bindungen theoretisch vorhergesagten Bindungswinkel ergibt sich, dass alle binären Übergangs-Aluminid-Halbleiter für die Al-Atome die gleiche Nahordnung aufweisen. Typische Werte für spezifische Widerstände der untersuchten Materialien bei Raumtemperatur liegen im Bereich von einigen 100µOhm cm, was weit größer ist als einige 10µOhm cm wie im Fall der unlegierten Metalle. Überraschend ist außerdem eine hohe Transportanisotropie mit einem Verhältnis der spezifischen Widerstände bis zu 3.0. Eine wesentliche Errungenschaft der Arbeit kann in der Verknüpfung der Eigenschaft des elektronischen Transports und der Bindungseigenschaften gesehen werden. Die geringen Leitfähigkeiten konnten durch geringe Werte in der Zustandsdichte (DOS) und einem bei gleicher Energie stattfindenden bindungs-antibindungs-Wechsel erklärt werden.

Ce mémoire porte sur l’étude théorique d’une réaction permettant la formation de macrocycles via une alkynylation de thiol catalysée au cuivre(I) (macro-CGS). Ce type de réaction implique le couplage entre un thiol et un carbone C(sp). Bien que le volet synthétique associé à cette réaction soit complété, jusqu’à ce jour aucune information n’existe concernant le mécanisme réactionnel. Des outils théoriques tels que la théorie de la fonctionnelle de la densité (DFT), la théorie de l’état de transition (TST) et les orbitales des liens naturels (NBO) ont été utilisés afin de mener cette étude à terme. Le mémoire comporte aussi un volet expérimental associé à la synthèse totale du macrocycle utilisé dans la réaction modèle. Le mémoire débutera avec une introduction portant sur la liaison de type S-C(sp) et sur les macrocycles. Nous introduirons ensuite en quoi consiste une étude théorique de mécanisme réactionnel. L’objectif du projet et la stratégie de recherche seront ensuite établis. L’introduction sera suivie d’un chapitre sur la méthodologie, dans lequel nous ferons un survol des concepts théoriques importants concernant le calcul de la structure électronique et la détermination des propriétés thermodynamiques d’un système chimique. Nous verrons ensuite les concepts théoriques importants qui ont été utilisés concertant la cinétique chimique et la modélisation de l’environnement chimique. Ce chapitre sera suivi de la justification du choix de la méthode computationnelle. Pour ce faire, différentes propriétés chimiques ont été prédites et comparées avec les résultats expérimentaux en utilisant différentes méthodes de calculs de structure électronique. Finalement, nous passerons aux résultats de la recherche, ce qui impliquera une courte section concernant la synthèse totale du macrocycle, une section concernant le profil énergétique des mécanismes examinés et une dernière section où nous proposerons une description des mécanismes les plus probables en se basant sur une analyse des orbitales de liaison naturelles (NBO). Les résultats de l’étude favorisent un mécanisme d’α-addition, mais un mécanisme d’α-cuprathiolation et d’addition oxydante - élimination réductrice seraient aussi à prendre en considération. Une étude expérimentale approfondie serait nécessaire afin de pouvoir obtenir plus d’informations concernant le mécanisme le plus probable. / This thesis is about the theoretical study of a reaction allowing the formation of macrocycles via Cu(I) -catalyzed S-C(sp) coupling to form a macrocyclic alkynyl sulfide. This type of reaction involves the coupling between a thiol and a C(sp) carbon. Although the synthetic part of that reaction is complete, to date, no information exists regarding the reaction mechanism. Theoretical tools such as density functional theory (DFT), transition state theory (TST) and natural bond orbitals (NBO) were used in order to undertake this study. The thesis also includes an experimental part associated with the total synthesis of the macrocycle used in the model reaction. The thesis will begin with an introduction on the S-C(sp) bond and on macrocycles in general. Afterwards, we will introduce the concept of theoretical study applied to a reaction mechanism. The goal and strategy of the study will then be established. The introduction will be followed by a chapter on the methodology, in which we make an overview of important theoretical concepts concerning electronic structure calculations and thermodynamic properties of a chemical system. We will then discuss theoretical concepts that have been used in concert with chemical kinetics and chemical environment. This chapter will be followed by a discussion on the choice of the computational method. For that purpose, different chemical properties were predicted and compared with experimental results using different electronic structure calculation methods. Finally, we will discuss the results of the study on the reaction investigated, which include a short section concerning the total synthesis of the macrocycle, a section concerning the energy profile of the studied mechanisms and a section where we provide a description of the most probable mechanisms based on a natural bond orbital (NBO) analysis. The results of the study are in favor of the α-addition mechanism, but the α-cuprathiolation and oxidative addition - reductive elimination mechanism should also be considered. Nevertheless, a thorough experimental study would be necessary in order to be able to obtain more information about the mechanism.