In this dissertation, we study the electronic and geometric structure of semiconductors and metal surfaces based on quantum mechanical first-principles calculations. We determine the geometry of vacancy defects of hydrogen adsorbed on a Pd(111) surface by treating the motion of a hydrogen atom, in addition to electrons, quantum mechanically. The calculated ground state wave function has high probability density in the hcp site located at the center of the vacancy instead of the fcc sites where the potential is minimum and hydrogen atoms on a Pd(111) surface normally adsorb. The geometry of quantum mechanically determined divacancy provides a simple and clear explanation for the scanning tunneling microscopy (STM) images of these defects that appear as three-lobed objects as observed in recent experiments [Mitsui, et al, Nature 422, 705 (2003)]. We employ the same principle to successfully elucidate the STM images of larger size vacancy defects. Our model also provides a compelling argument to explain the unusual recent experimental result that aggregates of three or more hydrogen vacancies are much more active in adsorption of hydrogen molecules while two-vacancy defects are never inactive. The InAs (110) surfaces appear lower than GaSb in STM images. This height difference is caused primarily by differences in the electronic structure of the two materials according to our calculations in a good agreement with measurements. In contrast, local variations in the apparent height of (110) surface atoms at InSb- or GaAs-like interfaces arise primarily from geometric distortions associated with local differences in bond length. The arsenic atoms adsorb preferably at the bridge sites between the dimerized Sb atoms on Sb-terminating (001) surfaces. Indium atoms, on the other hand, have somewhat equal probabilities at a few different sites on Ga-terminating (001) surfaces. Our calculated energies for atomic intermixing indicate that anion exchanges are exothermic for As atoms on Ga-terminating (001) interfaces but endothermic for In atoms on Sb-terminating (001) interfaces. This difference may explain why GaAs interfaces are typically more disordered than InSb interfaces in these heterostructures.

La question générale traitée dans cette thèse est de déterminer si, à l’heure actuelle, nous disposons d’outils théoriques efficaces pour décrire la structure, la liaison et les propriétés thermodynamiques de système comprenant un actinide. Cette large question va être abordée à l’aide de trois études différentes. Les deux premières sont directement liées à l’industrie plastique et à la sureté nucléaire. La dernière, plus fondamentale concerne une analyse comparative d’une approche théorique nouvellement développée sur des systèmes comprenant des éléments f. Tout d’abord, les cations alkyles contenant un actinide (Th, U) ou un métal de transition (Zr) coordonné à un arène se sont révélés efficaces pour la catalyse de la synthèse du polyéthylène. Étonnamment, les activités catalytiques des cations alkyles dépendent du solvant. Pour comprendre cela et confirmer la tendance qu’ont ces complexes à se lier à l’arène, une étude en DFT dans un contexte relativiste combinée à une caractérisation de liaison avec la méthode ETS-NOCV fut faite. La deuxième étude vise à étoffer les bases de données thermodynamiques qui servent à explorer numériquement les scénarios d’accidents. Notre étude in silico porte sur la détermination des enthalpies de formation des deux espèces pour lesquelles des incertitudes expérimentales subsistent (PuO3 ou PuO2(OH)2 …), en utilisant une méthode quantique multiconfigurationnelle et relativiste. La dernière partie de la théorie se concentre sur l’estimation de la précision de la fonctionnelle B2-PLYP pour les éléments f, qui s'avère assez précise en comparaison aux données expérimentales et à la méthode de référence CCSD(T). / The main question of this thesis is: do we have today the tools to efficiently describe the structure, the bonding and the thermodynamics of actinide systems? This broad question is answered thanks to three studies. The first two are directly applied to the plastic industry and the nuclear plant safety. The last one, more fundamental, concerns the benchmarking of newly developed theoretical approach on f-element systems.First, actinides and transition metal arene-coordinated alkyl cations have been recently proven to be efficient catalysts for ethylene polymerizations. Interestingly, thorium, uranium and zirconium alkyl cations’ catalytic activity depends on the solvent. To understand these behaviors and to confirm the tendency of these complexes to engage in unusual-arene coordination, relativistic DFT calculations combined with a characterization of the interaction thanks to the ETS-NOCV method are used. Second, in accident scenario along the reprocessing of spent nuclear fuel, plutonium can be released in various volatile forms (PuO2, PuO3 or PuO2(OH)2, …). The exploration of these scenarios by the use of simulations requires, among the various parameters, the knowledge of the thermodynamic properties of the possibly formed elements. Our in-silico study focusses on the determination of the enthalpies of formation of the former two species for which experimental uncertainties remain, using multi-configurational relativistic wavefunction method. The last part of the thesis focusses on the benchmark of the B2-PLYP functional for f-element systems, which turns out quite accurate with respect to the experimental data and the gold-standard CCSD(T) method.

Grafeno e nanofitas de grafeno vêm, cada vez mais, atraindo o interesse da comunidade científica devido as suas notáveis propriedades. Neste trabalho realizou-se um estudo sistemático da estabilidade de defeitos do tipo divacância, vacância e Stone-Wales em grafeno e nanofitas de grafeno com bordas zigzag. Para tal, fizeram-se cálculos de primeiros princípios, baseados em teoria do funcional da densidade (DFT) na aproximação GGA com o uso de pseudopotenciais ultrasoft e uma base de ondas planas. Também foram feitas simulações de imagens de STM para os defeitos nas nanofitas. Além disso, foram encontrados dois novos defeitos, não publicados em nenhum outro lugar (até onde vai o conhecimento do autor), com energia de formação muito baixa. / Graphene and graphene nanoribbons have been attracting a lot of interest from the scientific community because of their novel properties. In this work, a systematic research has been done on the stability and energetics of divacancy, vacancy and Stone-Wales defects in graphene and zigzag graphene nanoribbons. With this goal in mind, ab initio density functional calculations within the GGA approximation, using ultrasoft pseudopotentials and a plane wave basis were done. Also, STM images were simulated for some selected defects. Besides, two new defects, not published elsewhere (to the best knowledge of the author), with very low formation energy are reported.

La compréhension des phénomènes d’adsorption de gaz en présence d’eau dans des milieux confinés est une problématique importante tant d’un point de vue fondamental que du point de vue des applications industrielles Les travaux menés dans cette thèse ont principalement porté sur le développement d’un nouveau couplage NLDFT/SAFT-VR (Non-Local Density Functional Theory/ Statistical Associating Fluid Theory for potentials of Variable Range) pour modéliser les propriétés interfaciales et l’adsorption de méthane, d’eau et de leur mélange en milieu confiné. Les résultats théoriques obtenus sur ces fluides ont été comparés avec succès à des calculs de simulation moléculaire. Par ailleurs, des isothermes d’adsorption expérimentales de méthane et d’eau sur des charbons actifs ont été mesurées par la technique gravimétrique sur une balance à suspension magnétique. Afin de pouvoir comparer les isothermes expérimentales et théoriques, il est nécessaire de connaître la distribution en taille de pore des solides poreux. C’est pourquoi un nouveau modèle thermodynamique de caractérisation des milieux microporeux a été développé. Les comparaisons des isothermes d’adsorption de méthane ont montré un excellent accord entre résultats théoriques et expérimentaux. / Understanding the gas/water adsorption phenomena in confined media is an important issue from a fundamental point of view and for industrial applications. The main aim of this thesis was to develop a new NLDFT/SAFT-VR coupling (Non-Local Density Functional Theory/ Statistical Associating Fluid Theory for potentials of Variable Range) to model the interfacial properties and the adsorption of methane, water and their binary mixture in porous media. A successful comparison was found between theoretical results from this model and molecular simulation calculations. Moreover, experimental adsorption isotherms of methane and water were measured on activated carbons by gravimetric method on a magnetic suspension balance. In order to compare experimental and modeled adsorption isotherms, it is necessary to get the pore size distribution of the porous solids. To do this, a new thermodynamic model for the characterization of microporous media was developed. The comparison between adsorption isotherms of methane has shown an excellent agreement between theoretical results and experimental measurements.

Cette thèse porte sur la modélisation des propriétés structurales, aromatiques et spectroscopiques d'une nouvelle classe de macrocycles alternatifs aux porphyrines, les azacalixphyrines (ACPs). Ces macrocycles conjugués, synthétisés et caractérisés pour la première fois en 2010 par le groupe d’Olivier Siri à Marseille, ont montré des propriétés exceptionnelles (structure, absorption, tautomérie, et complexation). Cette thèse vise à proposer de nouveaux dérivés aux propriétés améliorées, notamment en ce qui concerne leur absorption, en utilisant les outils offerts par la chimie théorique. Parmi toutes les approches ab initio permettant de modéliser les ACPs, la théorie fonctionnelle de la densité (DFT) et sa forme dépendante du temps (TDDFT) ont été principalement appliquées, bien que des calculs utilisant des méthodes alternatives aient également été effectués, notamment à l'aide du formalisme Bethe-Salpeter (BSE/evGW) dans le cadre d'une collaboration avec l'équipe du Dr. Xavier Blase à Grenoble. Trois stratégies chimiques ont été évaluées: (i) l’extension de la délocalisation des électrons  en fusionnant plusieurs unités ACP; (ii) la substitution de l’ACP via l'addition de groupes électroactifs; et (iii) le couplage du macrocycle avec un fluorophore présentant une absorption complémentaire afin d'absorber la lumière sur une plus grande gamme du spectre et déclencher des processus de transfert d'énergie entre les sous-unités. Les deux premiers axes ont été réalisés en collaboration avec l'équipe d’Olivier Siri alors que le dernier est le fruit d'une collaboration avec le groupe de Benedetta Mennucci à Pise. / This thesis focuses on the modeling of the structural, aromatic, and spectroscopic properties of a new class of macrocycles alternative to porphyrins, i.e., azacalixphyrins (ACPs). These conjugated macrocycles have first been synthesized and characterized in 2010 by Siri’s group in Marseille and revealed exceptional features (structure, NIR absorption, tautomerism, and complexation). This thesis aimed at using ab initio methods to propose new ACP derivatives with improved properties with a focus on their absorption. The Density Functional Theory (DFT) and Time- Dependent DFT (TD-DFT) methods have been predominantly applied, although alternative wavefunction-based theories [the second-order Coupled-Cluster, CC2, and the Algebraic Diagrammatic Construction, ADC(2)] as well as the Bethe-Salpeter formalism, BSE/evGW, have also been used. Three major directions to develop new ACP derivatives have been investigated: (i) the extension of the ACP -conjugation path by fusing several ACP moieties leading to multimers; (ii) chemical modifications of the ACP unit by addition of electroactive groups; and (iii) coupling of the ACP moiety with a fluorophore presenting a complementary absorption spectrum in order to improve the light harvesting and to trigger excitation energy transfer processes. The two former axes have been investigated in collaboration with Siri’s team whereas the latter has arisen from a collaboration with the Mennucci’s group.

Grafeno e nanofitas de grafeno vêm, cada vez mais, atraindo o interesse da comunidade científica devido as suas notáveis propriedades. Neste trabalho realizou-se um estudo sistemático da estabilidade de defeitos do tipo divacância, vacância e Stone-Wales em grafeno e nanofitas de grafeno com bordas zigzag. Para tal, fizeram-se cálculos de primeiros princípios, baseados em teoria do funcional da densidade (DFT) na aproximação GGA com o uso de pseudopotenciais ultrasoft e uma base de ondas planas. Também foram feitas simulações de imagens de STM para os defeitos nas nanofitas. Além disso, foram encontrados dois novos defeitos, não publicados em nenhum outro lugar (até onde vai o conhecimento do autor), com energia de formação muito baixa. / Graphene and graphene nanoribbons have been attracting a lot of interest from the scientific community because of their novel properties. In this work, a systematic research has been done on the stability and energetics of divacancy, vacancy and Stone-Wales defects in graphene and zigzag graphene nanoribbons. With this goal in mind, ab initio density functional calculations within the GGA approximation, using ultrasoft pseudopotentials and a plane wave basis were done. Also, STM images were simulated for some selected defects. Besides, two new defects, not published elsewhere (to the best knowledge of the author), with very low formation energy are reported.

Les travaux décrits dans ce mémoire portent sur le calcul de la structure électronique de clusters homo- ou hétéro-nucléaires de métaux du groupe 11, afin d’en interpréter leur stabilité, leur structure et éventuellement leurs propriétés. Nous nous sommes tout d’abord intéressés au fait que, contrairement à leurs homologues de l’or et de l’argent, les superatomes de cuivre sont très rares. Nos calculs montrent que ces derniers sont plus stables que les superatomes d’argent. Néanmoins, les méthodes de synthèse de superatomes par réduction de complexes de Cu(I) par le borohydrure conduisent préférentiellement à la formation de polyhydrures de Cu(I) en raison de leur grande stabilité. Nous nous sommes de plus intéressés à la stabilité de clusters contenant un cœur tétraédrique M16, analogue à celui contenu dans le cluster emblématique [Au₂₀]. Notre étude des clusters organométalliques à 20 électrons. [M₁₆Ni₂₄(CO)₄₀]⁴⁻ (M = groupe 11) indiquent que les quatre entités périphériques Ni₆(CO)₁₀ font partie intégrante du superatome, suggérant que [M₁₆]⁴⁻ n’est pas viable. Des calculs sur plusieurs séries de systèmes homo- ou hétéro-nucléaires nus proposent de contourner cet écueil soit en réduisant le nombre d’électrons à 18, soit en incorporant un élément encapsulé au centre de l’entité tétraédrique. Dans une autre étude, nous avons exploré la possibilité de dopage du cluster icosaèdrique à 18 électrons [WAu₁₂] par des atomes de platine (donneurs de 0 électron), soit [WAu₁₂Pdₓ] (x = 1-4). Le calcul indique que certains isomères sont viables et présentent un large spectre d’absorption UV-vis leur conférant des applications potentielles. Enfin, nous avons étudié la structure électronique de clusters organométalliques apparemment très déficitaires en électrons, [Cu₃Zn₄Cp*5] et [Cu₂Zn₅Cp*₅]⁺ et montré que ce déficit n’est aussi important qu’il n’apparaît. / The work described in this manuscript concerns electronic structure calculations of homo- and hetero-nuclear clusters made of group 11 metals, in order to rationalize their stability, structure and in some cases properties. We have first looked at the fact that copper superatoms are very scarce, contrarily to their gold and silver counterparts. Our calculations indicate that copper superatoms are more stable than silver superatoms. However, the synthetic process based on the reduction of Cu(I) complexes by borohydride leads preferentially to the formation of very stable Cu(I) polyhydrides. On the other hand, we have looked at the stability of clusters containing a tetrahedral M₁₆ core similar to the one contained in the emblematic [Au₂₀] cluster. Our investigation of the 20-electron organometallic clusters [M₁₆Ni₂₄(CO)₄₀]⁴⁻ (M = group 11) showed that the four peripheral Ni₆(CO)₁₀ units are full part of the superatom entity, suggesting that the [M₁₆]⁴⁻ entity is not viable. Calculations on several homo- and hetero-nuclear series of bare species indicate that this instability can be avoided either in reducing the electron count to 18, or in incorporating a supplementary element in cluster center. In another investigation, we explored the possibility of doping the icosahedral 18-electron [WAu₁₂] cluster by 0-electron donor platinum atoms, namely [WAu₁₂Pdₓ] (x = 1-4). Calculations indicate that some isomers are stable and have a large spectrum of UV-vis absorption, providing them potential applications. Finally, we have investigated the electronic structure of organometallic clusters, [Cu₃Zn₄Cp*5] and [Cu₂Zn₅Cp*₅]⁺, which are apparently extremely electron-deficient and showed that this deficiency is not as large as it appears.

Density functional theory of statistical mechanics in a square gradient approximation was used to study nucleation in confined systems such as a cylindrical pore and in-between two cylindrical disks. This approximation was further applied to study the evaporation and condensation in nanopores with finite lengths. Confinement effects induced nucleation phenomena that are not observed in more open systems. Density functional theory was also used to explore the solvation properties of a spherical solute immersed in a supercritical diatomic fluid. The solute was modeled as a hard core Yukawa particle surrounded by a diatomic Lennard-Jones fluid represented by two fused tangent spheres using an interaction site approximation. The results of this study indicate that local density augmentation and the solvation free energies are particularly sensitive to changes in solute and solvent particle geometry and solute/solvent anisotropic interactions. Density functional theory allowed us to systematically study the effect of a variety of geometric and interaction parameters on the properties and behavior of all the systems. Although more sophisticated, but computationally more demanding, theoretical approaches can be used, our results provide fundamental physical insights into the behavior of real systems and create a solid basis for the development of more realistic models.

Density Functional Theory (DFT) is the most widely used theoretical tool for studying actinide complexes amongst the many available computational methods. However, the best choice of functional for theoretical actinide science is still not completely clear. Thus, benchmarking studies have been performed in this thesis in order to evaluate the performance of modern DFT applied to actinide systems. The first chapter is an introductory chapter which gives the background and the methods applied in this thesis. The second chapter is a part of the actinide spectroscopy Round-Robin test (RRT). The performance of DFT using different quantum chemistry programs with identical DFT functionals has been investigated by studying five U(VI) acetate complexes. The experimental data from the other clusters of RRT are used as reference for the quantum chemical calculations. The performance of a total of 22 different DFT functionals for small uranium complexes has been further investigated in Chapter 3. These functionals are compared by calculating geometries, vibrations frequencies, and reaction enthalpies against experimental data and high level ab initio CCSD(T) calculations. The last chapter presents a summary of the works in this thesis as well as directions for future studies. / May 2016

This thesis is dedicated to the development, implementation and application of a combination of Density Functional Theory and Dynamical Mean Field Theory. The resulting program is shown through several examples to be a powerful and flexible tool for calculating the electronic structure of strongly correlated materials. The main part of this work is focused on the development and implementation of three methods for solving the effective impurity model arising in the Dynamical Mean Field Theory: Hubbard-I approximation (HIA), Exact Diagonalization (ED), and Spin-Polarized T-matrix Fluctuation-exchange (SPTF). The Hubbard-I approximation is limited to systems where the hybridization between the 4f-orbitals and the rest of the material can be completely neglected, and can therefore not capture any Kondo physics. It has been used to study the atomic-like multiplet spectrum of the strongly localized 4f-electrons in the Lanthanide compounds YbInCu4, YbB12, Yb2Pd2Sn, YbPd2Sn, SmB6, SmSn3, and SmCo5. The calculated spectral properties are shown to be in excellent agreement with experimental direct and inverse photoemission data, clearly affirming the applicability of the Hubbard-I approximation for this class of systems if we are not focusing on Kondo physics. Full self-consistence in both self-energy and electron density is shown to be of key importance in the extraction of the magnetic properties of the hard permanent magnet SmCo5. The Exact Diagonalization solver is implemented as an extension of the Hubbard-I approximation. It takes into account a significant part of the hybridization between the correlated atom and the host through the use of a few effective bath orbitals. This approach has been applied to the long-standing problem of the electronic structure of NiO, CoO, FeO, and MnO. The resulting spectral densities are favorably compared to photoemission spectroscopy. Apart from predicting the correct spectral properties, the Exact Diagonalization solver also provides full access to the many-body density operator. This feature is used to make an in-depth investigation of the correlations in the electronic structure, and two measures of the quantum entanglement of the many-body ground-states are presented. It is shown that CoO possesses the most intricate entanglement properties, due to a competition between crystal field effects and Coulomb interaction, and such a mechanism likely carries over to several classes of correlated electron systems. The Exact Diagonalization solver has also been applied to the prototypical dilute magnetic semiconductor Mn doped GaAs, a material of great importance in the study of future spintronics applications. The problem of Fe impurities in Cs has been used to study the dependence of the spectral properties on the local environment. Finally, the Spin-polarized T-matrix Fluctuation-exchange solver has been implemented and applied to more delocalized electron systems where the effective impurity problem can be solved as a perturbation with respect to the strength of the local Coulomb interaction. This approach has been used to study the magnetic and spectral properties of the late transition metals, Fe, Co and Ni, and NiS.