L'objectif de cette thèse est de produire une avancée dans la compréhension du phénomène de fragilisation par les métaux liquide (FML), en nous appuyant sur l'étude expérimentale et numérique du couple cuivre/mercure. La fragilisation du cuivre pur OFHC (Oxygen Free High Conductivity) par le mercure liquide est mise en évidence et quantifiée par des mesures de ténacité. En outre, un procédé d'ingénierie des joints de grains est appliqué afin d'augmenter de façon importante la proportion de joints de grains spéciaux Σ3 dans le cuivre. Des essais de FML sont alors réalisés et permettent d'établir le rôle de ces joints de grains dans la fragilisation du cuivre par le mercure liquide. En parallèle, des modélisations de joints de grains spéciaux Σ3 et Σ5 sont réalisées par calcul basés sur la théorie de la fonctionnelle de la densité (DFT). Ces modélisations permettent à la fois de mettre en évidence une réduction des propriétés mécaniques de ces joints de grains en présence d'atomes de mercure, ainsi que de comprendre l'immunité des joints Σ3 observée expérimentalement. Cependant, ces modélisations ne permettent pas de rendre compte quantitativement des observations expérimentales. Pour améliorer cette description atomique de la FML, une contribution non locale est ajoutée, via l'utilisation d'un modèle de zone cohésive nourri par calcul DFT. Il est montré que le confinement du métal liquide en extrême pointe de fissure engendre une force normale aux parois de la fissure (l'origine physique de cette force est discutée), et que l'introduction de cette nouvelle composante permet de rendre compte des observations expérimentales de façon beaucoup plus quantitative. Ce dernier modèle est appuyé par la réalisation d'expériences de FML sous pression hydrostatique. / The aim of this thesis is to make an advance in the liquid metal embrittlement (LME) understanding, based on the experimental and numerical studies of the copper/mercury system. OFHC (Oxygen Free High Conductivity) copper embrittlement by liquid mercury is studied and quantified by toughness measures. Moreover, grain boundary engineering (GBE) is implemented in order to increase the proportion of special Σ3 grain boundaries. LME tests are performed and allow to establish the particular behaviour of the Σ3 grain boundaries in the copper embrittlement by liquid mercury. At the same time, modelling of special Σ3 and Σ5 grain boundaries based on density functional theory are performed. This allows to show the weakening of mechanical properties of both grain boundaries containing mercury atoms, and also to understand the immunity of Σ3 grain boundaries as observed experimentally. However, experimental observations can not been qualitatively explained by these modelling. In order to improve this description, a non-local contribution is introduced by means of a cohesive zone model. It is shown that the confinement of the liquid metal at the very crack tip produces a force normal to the surface of the solid (the origin of this force is discussed), and that the consideration of this force allows to describe more accurately experimental results. This model is supported by LME experiments under hydrostatic pressure.

This research is motivated by two significant challenges facing the planet: reducing the emission of CO2 to the atmosphere and production of sustainable fuels by harnessing solar energy. The main objective of this work is the study of promising photocatalysts for CO2 reduction. DFT modeling of CO2, subnanometer Ag&Pt clusters, and anatase TiO2 (101) surface is employed to gain fundamental understanding of the catalytic process, followed by validation using a guided experimental endeavor. The binding mechanism of CO2 on the surface is investigated in detail to gain insights into the catalytic activity and to assist with characterizing the photocatalyst. For CO2 photoreduction, the cluster induced sub-bandgap and the preferred adsorbate in the first and key step of the CO2 photoreduction are explored. It is found that TiO2-supported Pt octamers offer key advantages for CO2 photoreduction: 1. by providing additional stable adsorption sites for favored CO2 species in the first step, and 2. by aiding in CO2- anion formation. Electronic structure analysis suggests these factors arise primarily from the hybridization of the bonding molecular orbitals of CO2 with d orbitals of the Pt atoms. Also, structural fluxionality is quantified to investigate geometry dependent (3D-2D) CO2 adsorption. Geometric information, electronic information, and C-O bond breaking tendency of adsorbed CO2 species are proposed to connect to experimental observables (IR frequency). The CO2 adsorption sites on supported Pt clusters are also identified using IR as the indicator. A cluster-induced CO2 dissociation to CO pathway is also discovered. Finally, experimental work including dendrimer-encapsulated technique, TPD, and UV-Vis is performed to validate the computational results, the availability of adsorption sites and CO2 binding strength on supported Pt clusters.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Using first principles calculations based on the Density Functional Theory (DFT) with spin polarization and norm conserving fully separable pseudopotentials, we have studied the structural and electronic properties of the BC2N nanotubes and its interaction with oxygen atomic and molecular. The interaction with the atomic oxygen is investigated using substitutional and interstitial oxygen defects in type II BC2N nanotubes with two different chiralities: the armchair (3,3) and the zigzag (5,0). The interaction with the oxygen molecular is investigated by the adsorption of the O2 in the inner and outer surfaces of a type II armchair (3,3) BC2N nanotube. Our results show that the oxygen in the nitrogen site (ON) is the most favorable site for the substitutional oxygen defect and the electronic properties are similar for the two nanotubes, and shallow donor levels are observed. For the interstitial oxygen defects, the oxygen between the bond of boron and CI carbon (B-O-CI) is the most favorable site and electronic properties are only slightly modified compared with the pristine systems. For the interaction of oxygen molecular with a armchair (3,3) BC2N nanotube, the most stable configuration is obtained for the O2 molecule in the inner surface and perpendicular to the nanotube axis. This configuration is also more stable, considering the Van der Waals interactions between the nanotube and the O2 molecule in the calculation of binding energies. The electronic properties are not changed. We conclued that the interaction between the (3,3) nanotube and the O2 molecule is a phy-sical process, ruled by the Van der Waals interactions. / Utilizando cálculos de primeiros princípios fundamentados na Teoria do Funcional da Densidade (DFT) com polarização de spin e pseudopotenciais de norma conservada, estudamos as propriedades estruturais e eletrônicas de nanotubos de BC2N e a sua interação com oxigênio atômico e molecular. A interação com oxigênio atômico foi investigada através de defeitos de oxigênio substitucional e oxigênio intersticial em nanotubos de BC2N do tipo II com duas quiralidades diferentes: armchair (3,3) e zigzag (5,0). A interação com oxigênio molecular foi investigada através da adsorção de uma molécula de O2 na superfície interna e externa de um nanotubo de BC2N armchair (3,3) do tipo II. Nossos resultados mostram que o oxigênio no sítio do nitrogênio (ON) é o sítio mais favorável para o defeito de oxigênio substitucional e as propriedades eletrônicas apresentam características semelhantes para os dois nanotubos e níveis doadores rasos estão presentes. Para o defeito de oxigênio intersticial, o oxigênio entre a ligação de boro e de carbono CI (B-O-CI) é o sítio mais favorável e as propriedades eletrônicas apresentam poucas modificações em comparação com os sistemas pristina. Para a interação de oxigênio molecular com um nanotubo de BC2N armchair (3,3), a configuração mais estável é obtida para a molécula de O2 adsorvida internamente e perpendicularmente ao eixo do nanotubo (3,3). Esta configuração também é a mais estável, considerando as interações de Van der Waals entre o nanotubo e a molécula de O2 no cálculo das energias de ligação. As propriedades eletrônicas são pouco modificadas pela presença da molécula de O2, ou seja, apresentam dois níıveis de spin down no gap de energia que estão localizados na molécula de O2. Concluímos que a interação entre o nanotubo (3,3) e a molécula de O2 é uma interação física, tipo interação de Van der Waals.

Les matériaux hybrides organiques-inorganiques forment une classe de systèmes dans lesquels plusieurs types de molécules organiques peuvent être insérées au sein d'une structure dite d’accueil, souvent de nature inorganique. C'est dans ce contexte que s'inscrit notre étude théorique de ces matériaux, utilisant les méthodes de la théorie de la fonctionnelle de la densité (DFT), jointes aux techniques de dynamique moléculaire (MD) dans l'approche dite de dynamique moléculaire ab initio. Nous avons développé un protocole permettant d'étudier l'évolution des propriétés de matériaux hybrides spécifiques sous l'effet de stimuli extérieurs comme la pression ou la température. Nous effectuons une étude théorique d’un matériau de référence dans la chimie des matériaux hybrides lamellaires: l'hydroxyde acétate de cuivre Cu2 (OH)3 (CH3 COO). Nous avons obtenu une transition d’un état antiferromagnétique à un état ferromagnétique sous l’effet d’une pression proche de 2 GPa, en bon accord avec la valeur expérimentale (1,2 GPa). Ensuite, nous appliquons ces méthodes à l’étude de nouveaux matériaux hybrides lamellaires simples contenant des molécules de fluorènes mono- et di- phosphoniques. / Ab-initio molecular dynamics (AIMD) refers to a set of state-of-the-art computational methods combining molecular dynamics with density functional theory. It is the basis of what could be called a «Virtual laboratory approach». In this work, we use the Car-Parrinello Molecular Dynamics (CPMD) scheme for investigating the properties of Copper Hydroxide Acetate system, a typical organic-inorganic hybrid material. We determine the corresponding atomic structure as well as several of its chemical and magnetic properties. Recent experimental achievements provide accurate XRD measurements enabling the study of magneto-structural properties of Cu2 (OH)3 (CH3 COO). compound. The pressure-induced magnetic transition, observed experimentally (at 1,2 GPa) in this material has been successfully reproduced (close to 2 GPa), thereby, highlighting the role of structural optimizations in theoretical treatments of such materials. Our aim is to elucidate the complex interplay between structural properties, interfacial inte r facial chemistry and magnetic behaviors of various nanoscale structured materials both at the local (atomic) and bulk (crystal) levels. We focus on copper hydroxide-based hybrid materials spanning through different organic components (such as fluorene mono- or di-phosphonic molecules) considered prototypical and very promising in the field of hybrid multifunctional materials.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / A study of InP nanowires with an oxide layer, as well as the initial steps of the oxidation process is pursued through first principles calculations and molecular dynamics simulations within the Density Functional Theory. An InP nanowire in the wurtzite phase in an environment containing a O2 molecular gas is used to simulate the initial steps of the nanowire oxidation process. The molecular dynamics simulations reveal that the O2 molecules dissociate preferentially in reactions with the P atoms and that that they are incorporated into the nanowire, mainly at the superficial layers. The molecular dynamics simulation of the already oxidated InP nanowire reveals a pair distribution function very close to that of the pure nanowire, although there is a disarrangement of the local crystalline phase. The defects generated by the atoms lead to the closure of the energy gap, due mainly to the contribuition coming rom the In atoms bond to oxygen. / Um estudo de nanofios de InP oxidados, assim como das etapas iniciais do processo de oxidação é realizado usando cálculos de primeiros princípios e dinâmica molecular a 300K, dentro da Teoria do Funcional da Densidade. Um nanofio de InP na fase wurtzita num ambiente contendo um gás de moléculas O2 é usado para simular as etapas iniciais do processo de oxidação do nanofio. A dinâmica molecular revela que as moléculas de O2 se dissociam preferencialmente em reações com átomos de P, com os átomos de oxigênio sendo incorporados em suas camadas superficiais. A simulação de dinâmica molecular do nanofio de InP já oxidado revela uma função distribuição de pares muito próxima à do fio puro, embora haja desestruturação da fase cristalina local. Os defeitos gerados pela presença dos átomos de oxigênio levam a um fechamento do gap de energia, devido principalmente à contribuições vindas dos átomos de In ligados ao oxigênio.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In this thesis we performed a theoretical study of the structural, electronic, and magnetic properties of transition metal (TM) particles using two models, with 13 and 55 atoms to describe clusters, nanoparticles (NPs), nanoalloys, protected NPs, and adsorption on clusters by Density Functional Theory. Firstly, we performed a systematic study for 3d, 4d, and 5d TMs of the Periodic Table using clusters with 13 atoms. This study gives the trends of the properties as function of the d occupation. We implemented a strategy to obtain the clusters structures, which is based on high-temperature molecular dynamic calculations and simulated annealing. New lower energy configurations were identified for some 13 atom clusters and previous known structures were confirmed. The following conclusions were identified: (i) The analysis of the binding energies and average bond lengths show a parabolic-like shape as a function of the occupation of the d states and hence, most of the properties can be explained by the chemistry picture of occupation of the bonding and antibonding states. (ii) Ground state structures are seen to depend on the d band occupation, with compact icosahedral-like (ICO) forms at the beginning of each metal series, more opened structures such as hexagonal bilayer-like (HBL) and double simple-cubic (DSC) layers at the middle of each metal series, and structures with an increasing effective coordination number occur for large d states occupation. (iii) For Au13, we found that spin-orbit coupling favors 3D structures, i.e., a 3D structure is about 0.10 eV lower in energy than the previously assumed lowest energy 2D configuration. (iv) The magnetic exchange interactions play an important role for particular systems such as Fe, Cr, and Mn. Several trends are similar for clusters and bulk, however, the atomic structures for Ru13, Rh13, Os13, and Ir13 are considered unexpected, since the respective elemental crystals crystallize in compact structures. In this context, we employed different local, semilocal, and non-local exchange and correlation energy functional, to understand the performance of different exchange and correlation schemes in the prediction of the physical and chemical properties of TM clusters. The local and semilocal functionals confirm the DSC configuration as the lowest energy structure for the studied TM13 clusters. A good agreement in the relative total energies is obtained even for structures with small energy differences, i.e., the PBE (Perdew, Burke, and Ernzerhof) results are confirmed. With the study employing PBE+U and hybrid functionals we found that a partial correction of the self-interaction problem decreases the relative stability of opened structures such as the DSC, and hence, compact structures became the lowest energy ones. The sd hybridization helps to explain the dependence of the structural stabilities with the self-interaction correction. We found that, for Co13 and Rh13, the sd hybridization decreases for DSC and increases for ICO. The study of NO adsorption on TM13 clusters, such as: Rh13, Pd13, Ir13 and Pt13, and the comparison with the results obtained for the respective TM(111) surfaces, allowed the finding that the adsorption on clusters changes significantly, with a strong dependence of the chemical environment close to the adsorption sites, whereas the trend obtained for the characteristic geometric parameters are similar to those observed for NO/TM (111). For the TM55 we get that Co55 and Rh55 NPs have ICO lowest energy structures, contrarily to the respective 13 atoms clusters. For Pt55 and Au55 NPs we found a non-icosahedral structure, with lower symmetry and the reduced core size, 7 - 9 atoms, which is very important for catalysis due to the larger number of atoms at the surface. After the TM55 study, we performed the study for PtnTM55-n (TM = Co, Rh, Au) nanoalloys as a function of the composition (n). It is confirmed that PtTM NPs prefer a composition pattern where the Co and Rh (Pt) atoms are in the core region and Pt (Au) atoms are at the surface region. Furthermore, we get that PtnRh55-n and, especially, PtnCo55-n tend to form alloys, mainly between n = 28 42 and n = 20 42, where the core-shell ICO configurations (Pt42Co13 and Pt42Rh13) are stable for both systems, due to the different atomic sizes that cause a release of stress in the NPs. For PtnAu55-n nanoalloys only n = 13 is energetically favorable, forming a core-shell structure. For the other compositions of PtAu we have the same trend as for the crystalline alloys reported experimentally, i.e., non-alloy formation. The effects on the catalytic properties of mixing two-TMs can be understood through the shift of the gravity center of the d occupied states. In this analysis, we observed that it is possible to obtain PtTM nanoalloys that can be more affordable and have better catalytic properties than pure Pt NPs. In terms of magnetic properties, we found that Pt55 and Co55 have smaller and larger values of magnetic moments, respectively, so PtCo follows the tendency where the Co atoms dominate the magnetic properties. For PtRh, the magnetic moment values are higher than for pure NPs. In the case of PtAu we observed the same trend, although with a lower magnitude. The lowest energy structures for Pt55 and Au55 are non-icosahedral, with an unexpectedly small core. Thus, we study these systems adding ligands, and verifying the changes in the stability. We studied the interaction of TM NPs with ligands such as: PH3, PH2, and SH2, in order to verify the changes in stability, structural, and electronic properties. We obtained that the relative stability differences between ICO and LOW (lowest energy configuration) structures decreases with the use of ligands. The LOW structures are not the most stable (Au) or very similar in energy than ICO structures (Pt) when 18 ligands are added to NPs. / Nesta tese de doutorado realizou-se o estudo teórico das propriedades estruturais, eletrônicas e magnéticas de partículas de metais de transição (TMs) utilizando modelos com 13 e 55 átomos para descrever clusters, nanopartículas (NPs), nanoligas, NPs protegidas por ligantes e adsorção sobre clusters, via Teoria do Funcional da Densidade. Primeiramente, realizou-se um estudo sistemático dos TMs 3d, 4d e 5d da Tabela Periódica usando o modelo de clusters com 13 átomos. Este estudo possibilitou a obtenção de tendências nas propriedades dos clusters em relação à ocupação dos estados d. Fazendo-se uso de uma estratégia de obtenção de estruturas de mais baixa energia baseada em simulações de dinâmica molecular e simulated annealing, foi possível não só obter as estruturas mais estáveis reportadas na literatura, mas também novas configurações de mais baixa energia ainda não reportadas. As seguintes conclusões foram obtidas: (i) A energia de ligação e o comprimento médio de ligação possuem uma curvatura parabólica em função da ocupação dos estados d e, assim, muitas das propriedades podem ser explicadas pelo modelo de níveis ligante e antiligante. (ii) Estruturas compactas do tipo icosaédricas (ICO) são energeticamente favoráveis no início de cada série; estruturas mais abertas, tais como bicamada hexagonal (HBL) e cúbica simples dupla (DSC) são energeticamente favoráveis no meio de cada série e estruturas com um alto número de coordenação ocorrem para grandes ocupações dos estados d. (iii) Para o caso específico de Au13, verificou-se que o acoplamento spin-órbita favorece estruturas 3D, ou seja, a estrutura 3D é 0,10 eV mais estável que a configuração de mais baixa energia 2D, a qual era tida como a mais estável na literatura. (iv) As interações de troca magnética possuem um importante papel para sistemas tais como Fe, Cr e Mn. Verificou-se que muitas tendências são compartilhadas por clusters e os respectivos cristais. Estruturas inesperadas (DSC), abertas e com baixa coordenação, foram obtidas para Ru13, Rh13, Os13 e Ir13, contrastando com os cristais, que possuem estruturas fechadas. A excepcionalidade destas estruturas abertas levou-nos a investigar a influência de diferentes aproximações para o termo de troca e correlação (locais, semilocais e não locais) na determinação das estruturas de equilíbrio destes clusters. O emprego de funcionais locais e semilocais confirmou a estrutura DSC como sendo a mais estável e apresentou boa concordância nas energias relativas obtidas, mesmo para estruturas com pequenas diferenças de energia, ou seja, confirmou-se os resultados obtidos com o funcional PBE (Perdew, Burke e Ernzerhof). No entanto, o emprego de abordagens utilizando as aproximações PBE+U e funcional híbrido aplicados para alguns sistemas, mostrou que o aumento da localização eletrônica influencia diretamente a estabilidade dos clusters. A correção parcial do problema de auto-interação aumenta a estabilidade das estruturas fechadas. A hibridização sd auxilia na explicação da estabilidade estrutural, já que esta decresce para as configurações DSC e aumenta para as ICO. O estudo da adsorção da molécula de NO sobre alguns dos TM13 de maior interesse na literatura: Rh13, Pd13, Ir13 e Pt13 e a comparação com os resultados obtidos para as respectivas superfícies de TM(111) possibilitou a constatação de que a adsorção sobre os clusters varia significativamente, com forte dependência do ambiente químico próximo aos sítios de adsorção; enquanto que as tendências obtidas para os parâmetros geométricos característicos são similares aos observados para NO/TM(111). Do estudo de TM55 obteve-se que as NPs de Co55 e Rh55 possuem a estrutura ICO como sendo a mais estável, enquanto que estruturas HBL e DSC foram obtidas respectivamente para Co13 e Rh13. Já para Pt55 e Au55 uma estrutura não-icosaédrica é obtida como sendo a mais estável, com baixa simetria e com o tamanho de caroço reduzido, 7 9 átomos, fato que tem conseqüências diretas para aplicações em catálise, devido a maior quantidade de átomos na superfície. Após o estudo de NPs de TM55 estudou-se nanoligas de PtnTM55-n (TM = Co, Rh, Au) em função da composição (n), verificou-se que as NPs de PtTM preferem um padrão de composição com os átomos de Co ou Rh (Pt) na região do caroço e os átomos de Pt (Au) na região de superfície. Obteve-se que PtnRh55-n e, especialmente, PtnCo55-n tendem a formar ligas, principalmente entre n = 28 42 e n = 20 42, sendo que as configurações core-shell ICO (Pt42Co13 e Pt42Rh13) são estáveis para esses sistemas, devido a diminuição do stress causada pelas diferenças de tamanhos atômicos. Já para PtnAu55-n apenas a composição n = 13 é favorável (estrutura core-shell), as demais composições não são favorecidas energeticamente, da mesma forma como ocorre para as fases cristalinas. Mostrou-se que os efeitos da mistura de dois TMs nas propriedades catalíticas podem ser entendidos por meio do deslocamento do centro de gravidade dos estados d ocupados. Desta análise, observou-se a possibilidade de obtenção de nanoligas PtTM que podem ser mais acessíveis economicamente e ter melhores propriedades catalíticas que NPs puras de Pt. Obteve-se que Pt55 e Co55 possuem baixos e altos valores de momento magnético, respectivamente, logo PtnCo55-n segue uma tendência onde os átomos de Co dominam o comportamento magnético. Para PtRh observou-se valores de momento magnético algumas vezes maiores que para as NPs puras e para o caso de PtAu temos a mesma tendência, porém em menor magnitude. Devido as estruturas inesperadas obtidas para as NPs Pt55 e Au55 estudou-se esses sistemas, acrescentando ligantes (PH3, SH2 e PH2), verificando assim, as alterações na estabilidade. Obteve-se que a diferença de estabilidade relativa entre as estruturas ICO e LOW (configuração de mais baixa energia) diminui com o emprego de ligantes. As estruturas LOW deixam de ser as mais estáveis (Au) ou ficam muito próximas em energia da estrutura ICO (Pt) quando 18 ligantes são adicionados às NPs.

La théorie de la fonctionnelle de la densité classique est utilisée pour étudier la solvatation de solutés quelconques dans le solvant eau. Une forme approchée de la fonctionnelle d’excès pour l’eau est proposée. Cette fonctionnelle nécessite l’utilisation de fonctions de corrélation du solvant pur. Celles-ci peuvent être calculées par simulations numériques, dynamique moléculaire ou Monte Carlo ou obtenues expérimentalement. La minimisation de cette fonctionnelle donne accès à l’énergie libre de solvatation ainsi qu’à la densité d’équilibre du solvant. Différentes corrections de cette fonctionnelle approchée sont proposées. Une correction permet de renforcer l’ordre tétraédrique du solvant eau autour des solutés chargés, une autre permet de reproduire le comportement hydrophobe à longue distance de solutés apolaires. Pour réaliser la minimisation numérique de la fonctionnelle, la théorie a été implémentée sur une double grille tridimensionnelle pour les coordonnées angulaires et spatiales, dans un code de minimisation fonctionnelle écrit en Fortran moderne, mdft. Ce programme a été utilisé pour étudier la solvatation en milieu aqueux de petits solutés atomiques neutres et chargés et de petites molécules polaires et apolaires ainsi que de solutés plus complexes, une argile hydrophobe et une petite protéine. Dans chacun des cas la théorie de la fonctionnelle de la densité classique permet d’obtenir des résultats similaires à ceux théoriquement exacts obtenus par dynamique moléculaire, avec des temps de calculs inférieurs d’au moins trois ordres de grandeurs. / A classical density functional theory is applied to study solvation of solutes in water. An approx- imate form of the excess functional is proposed for water. This functional requires the knowledge of pure solvent direct correlation functions. Those functions can be computed by using molecular simulations such as molecular dynamic or Monte Carlo. It is also possible to use functions that have been determined experimentally. The functional minimization gives access to the solvation free energy and to the equilibrium solvent density. Some correction to the functional are also proposed to get the proper tetrahedral order of solvent molecules around a charged solute and to reproduce the correct long range hydrophobic behavior of big apolar solutes. To proceed the numerical minimization of the functional, the theory has been discretized on two tridimensional grids, one for the space coordinates, the other for the angular coordinates, in a functional mini- mization code written in modern Fortran, mdft. This program is used to study the solvation in water of small solutes of several kind, atomic and molecular, charged or neutral. More complex solutes, a neutral clay and a small protein have also been studied by functional minimization. In each case the classical density functional theory is able to reproduce the exact results predicted by MD. The computational cost is at least three order of magnitude less than in explicit methods.

Les argiles sont utilisées dans de nombreuses applications industrielles pour lesquelles l’étude des interactions entre l’eau et les matériaux argileux sont primordiales. Les mécanismes de rétention et de transport de l'eau et des ions à la surface des argiles peuvent être modélisés à l'échelle atomique grâce à des méthodes classiques comme la Dynamique Moléculaire. Ces méthodes nécessitent de paramétrer au préalable les interactions entre les atomes du système. L'objectif principal de cette étude est d'améliorer la description de ces systèmes via la paramétrisation d'un nouveau champ de force polarisable entièrement basée sur des calculs issus de la méthode de la Théorie de la Fonctionnelle de la Densité. Les propriétés structurales, thermodynamiques et dynamiques de la pyrophyllite, du talc, et de la Na-, Ca-, Sr- et Cs-montmorillonite (sèches et hydratées) ont été bien reproduites. Notamment, la structure des couches tétraédriques et celle des espaces interfoliaires sont en très bon accord avec les données expérimentales. / The wide use of clay minerals in industrial applications is partly due to their remarkable properties of water retention at the mineral surface. Retention and transport mechanisms of water molecules and ions at the surface of clays can be modeled at the atomic scale via different classical methods such as molecular dynamics. These methods require to parametrize in advance the interaction between the atoms of the system. The goal of this study is to improve the description of these systems via the parametrization of a new polarizable force field entirely based on density functional theory calculations.The structure, the thermodynamics and the dynamics properties of pyrophyllite, talc and Na-, Ca-, Sr- and Cs-montmorillonite are well reproduced. The atomic structure of sheets and interfoliar space are in good agreement with experimental results.

Abstract This thesis presents computational first-principles investigations of nuclear magnetic resonance (NMR) parameters in metal-containing nanosystems. Special attention is paid to the relativistic effects observed in the vicinity of heavy elements. Small transition metal complexes are used to assess the feasibility of a quasirelativistic density functional theory (DFT) approach for calculating nuclear magnetic shielding tensors of increasingly heavy metal nuclei, followed by applications of the concept to larger systems. Nuclear magnetic shielding constants, shielding anisotropies, and chemical shifts with respect to metal ions are calculated in dimethyl and water complexes of the group-12 transition metals 67Zn, 111/113Cd, and 199/201Hg, using Hartree–Fock and DFT methods with relativistic corrections from the Breit–Pauli Perturbation Theory (BPPT). Four-component relativistic Dirac–Hartree–Fock and correlated, nonrelativistic ab initio calculations are used to benchmark the BPPT and DFT methods, respectively. The DFT/BPPT approach, combined with Monte Carlo simulations at finite temperatures, is subsequently used to calculate the chemical shift of a guest 129Xe inside a tetrahedral, iron-based cage. Complementing experiments, the encapsulation of xenon is verified, and empirically elusive details are revealed about the guest dynamics. Finally, the full shielding tensors of 31P and 195Pt and the indirect spin–spin coupling constants between the two nuclei are studied in five crystalline platinum(II) dialkyldithiophosphato complexes, concentrating on the solid-state chemical shift anisotropy and asymmetry parameters of phosphorus and platinum. The NMR parameters are calculated using DFT and the two-component zerothorder regular approximation (ZORA) for relativistic effects, combining molecular and solid-state models to incorporate indispensable contributions due to spin–orbit and crystal lattice corrections for the shielding tensors. Four-component matrix-Dirac–Kohn–Sham shielding calculations are used to benchmark the ZORA method. Qualitative, in cases nearly quantitative agreement is obtained with experiments, allowing the validation of the X-ray structures of the complexes, as well as a deeper analysis of the differences between them, including the major contributions to the NMR parameters. The results presented here demonstrate that computational NMR, a branch of relativistic quantum chemistry, is applicable and useful in studying nanoscale systems containing heavy elements, such as transition metals. Approximations are necessary to enable the treatment of large and complex targets, but sufficient accuracy is achieved for supplementing experiments with reliable and useful data that provides additional insight and analysis possibilities.

Ce manuscrit de thèse est dédié aux calculs quantiques de paramètres de spectroscopie de résonance magnétique nucléaire (RMN) de métaux de transition dans des composés inorganiques de l’état solide. Le manuscrit est divisé en cinq parties. La première partie présente les atouts de la spectroscopie RMN en tant que technique d’investigation de composés inorganiques de l’état solide. Dès lors que le noyau sondé est un métal de transition, l’expérience doit être complétée par des calculs quantiques afin d’interpréter au mieux les données expérimentales. La seconde partie du manuscrit est dédiée à la description de la RMN et des outils méthodologiques utilisés dans ce travail. Le troisième chapitre est dédié au calcul du déplacement chimique de l’isotope 95 du molybdène dans des clusters halogénés de formule [Mo6X14]2- (X = Cl, Br, I). Une attention particulière est donnée à l’influence des effets de solvatation sur le calcul. Le quatrième chapitre est dédié à l’étude des composés A6Re3Mo3S8(CN)5 (A = K, Cs) dont la structure cristallographique est basée sur un motif octaédrique hétéronucléaire Re3Mo3S8(CN)6. La résolution structurale par diffraction des rayons X sur monocristal n’ayant pas permis de résoudre le problème de la distribution des métaux de transition dans l’octaèdre, une étude spectroscopique in silico sur la base de calculs DFT moléculaires et périodiques a été entreprise. Dans le dernier chapitre, des composés hétéronucléaires de formule [Ln6-6xLn6xO(OH)8(NO3)6(H2O)12]2+ (Ln = Pr-Lu, Y) ont été étudiés du point de vue théorique afin de mieux comprendre les données spectroscopiques collectées. / This work is devoted to the calculations of nuclear magnetic resonance (NMR) parameters of transition metal nuclei in inorganic solid-state materials using first-principles calculations. The manuscript is divided in five chapters. The first one shows that NMR is an interesting spectroscopic method to gain some information on the properties of inorganic materials. As far as the probed nucleus is a transition metal, experiments must be completed with quantum chemical calculations in order to better interpret the spectroscopic data. The second chapter is devoted to the quantum chemical tools that are necessary to the understanding of this work are presented. The third chapter deals with the computations of 95Mo NMR parameters of [Mo6X14]2- (X = Cl, Br, I) octahedral clusters. A special attention is paid to the influence of solvation effects on the computed NMR parameters. The fourth chapter is devoted to the study of A6Re3Mo3S8(CN)5 (A = K, Cs) compounds. Their crystal structures are based on a heteronuclear octahedral motif Re3Mo3S8(CN)6. Since X-ray diffraction refinements did not solve the colouring problem in the octahedron, an in silico spectroscopic study has been carried out using molecular and periodic DFT calculations. The last chapter of this report deals with heteronuclear polyoxolanthanides that have been studied using first-principles calculations in order to better understand their 89Y NMR spectra.