Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-07-20T19:28:19Z No. of bitstreams: 1 florencepereiranovaisantunes.pdf: 2879839 bytes, checksum: 7b30047152e7859559f55c0751ebe824 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-08-09T13:28:00Z (GMT) No. of bitstreams: 1 florencepereiranovaisantunes.pdf: 2879839 bytes, checksum: 7b30047152e7859559f55c0751ebe824 (MD5) / Made available in DSpace on 2017-08-09T13:28:00Z (GMT). No. of bitstreams: 1 florencepereiranovaisantunes.pdf: 2879839 bytes, checksum: 7b30047152e7859559f55c0751ebe824 (MD5) Previous issue date: 2010-03-10 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O estudo da degradação de organofosforados é de suma importância tanto na área ambiental quanto na de defesa química. Tem sido descrito na literatura exaustivos estudos sobre degradação de organofosforados relacionados à agricultura. Um desses estudos leva em conta o uso da luz na degradação de um dos organofosforados mais usados na agricultura como pesticida, o paration. O processo chamado de fotocátalise heterogênea, envolve a ativação de um semicondutor (geralmente TiO2) por luz solar ou artificial. A absorção de fótons com energia superior à energia de “bandgap” resulta na promoção de um elétron da banda de valência para banda de condução com geração concomitante de um buraco (hole) na banda de valência. Estes buracos mostram potenciais suficientemente positivos, capazes de formar radicais hidroxila a partir de moléculas de água adsorvidas na superfície do semicondutor, os quais podem subseqüentemente oxidar contaminantes orgânicos. O objetivo deste trabalho foi determinar a influência da substituição de titânio por zircônio em TiO2 na adsorção de organofosforados, que é uma das etapas de degradação desses compostos. Para isso foram determinadas as estruturas, propriedades eletrônicas e vibracionais de organofosforados adsorvidos em TiO2 (101) anatase e Ti(1-x)ZrxO2. Os compostos estudados e adsorvidos são: Paration, Sarin e VX. A idéia foi propor uma técnica bem descrita experimentalmente para degradação do paration, para possível detoxificação de organofosforados usados como armas químicas, no caso, o Sarin e o VX. Foi feito o estudo da adsorção dos organofosforados em titânia substituída com zircônio na proporção Ti(1-x)ZrxO2, levando em conta que modificações na estrutura do catalisador aumentam a atividade fotocatalítica. Cálculos feitos verificam a contribuição energética da etapa de adsorção e comparando com a estrutura do catalisador puro foi possível obter melhora nesta etapa. Foram obtidas energias de fisissorção e quimissorção nas diferentes posições possíveis. O tipo de adsorção foi confirmado com estudos de diferença de carga eletrônica. Foi obtido também o estudo de frequência vibracional. A partir dos resultados, concluiu-se que a adsorção se processou de maneira mais efetiva nos casos em que foi usado o catalisador com zircônio, com energia de adsorção de -25,71kcal/mol, para o p-VX adsorvido. Em titânia pura a energia de adsorção de p-VX foi de -18,14kcal/mol. As diferenças de densidade de carga eletrônica também confirmaram os resultados. / The study of degradation of organophosphorous is critical both in the environmental area as in chemical defense. Has been described in the literature studies on degradation of organophosphorous related to agriculture. One of the study considers the use of light in a degradation of the organophosphorous pesticide used in agriculture: the parathion. The process called heterogeneous photocatalysis involves the activation of a semiconductor (usually TiO 2) by sunlight or artificial. The absorption of photons with energy higher than the energy band gap results in the promotion of an electron from the valence band to conduction band with concomitant generation of a hole (hole) in the valence band. These holes show sufficiently positive potential, capable of forming hydroxyl radicals from water molecules adsorbed on the semiconductor surface, which can subsequently oxidize organic contaminants. The aim of this study was to determine the influence of the substitution of titanium by zirconium in TiO2 adsorption of organophosphorous, which is one of the stages of degradation of these compounds. For this we determine the structures, vibrational and electronic properties of organophosphorous adsorbed on TiO2 (101) anatase and Ti(1-x)ZrxO2. The compounds adsorbed are: parathion, sarin and VX. The idea was to propose a technique well described experimentally for the degradation of parathion for possible detoxification of organophosphorous used as chemical weapons, in this case, Sarin and VX. Was done to study the adsorption of organophosphorous in titania replaced with zirconium in the ratio Ti(1-x)ZrxO2, taking into account that changes in the structure of the catalyst increase the photocatalytic activity. Calculations verify the contribution of the adsorption energy step and comparing the structure of the pure catalyst was possible to obtain improvement in this step. We obtained energies of physisorption and chemisorption at different possible positions. The type of adsorption was confirmed with studies of in electronic difference charge. Was also obtained to vibrational frequency study. From the results it was concluded that the adsorption is processed more effectively in cases where the catalyst was used with zirconium, with adsorption energy of -25.71 kcal / mol for p-VX adsorbed. Titania in pure energy of adsorption, p-VX was -18.14 kcal / mol. The difference in electronic charge density also confirmed the results.

Orientador: Douglas Soares Galvão / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-19T14:34:16Z (GMT). No. of bitstreams: 1 Autreto_PedroAlvesdaSilva_D.pdf: 59520269 bytes, checksum: 40cf8840fce242581f34d0cee4cd3dda (MD5) Previous issue date: 2011 / Resumo: A nanotecnologia teve seu início simbólico na apresentação de 1959 do Prêmio Nobel Richard Feynman: \"Há muito espaço lá embaixo\". Nesta palestra Feynman destaca as possibilidades de criação de novos materiais, desenhados para possuírem determinadas propriedades eletrônicas e estruturais. Desde então, grandes avanços têm sido feitos e estruturas antes nunca imaginadas têm sido observadas e produzidas. Estas são compostas dos mais diferentes materiais, desde os metais até carbono. Como exemplo de compostos de metais temos os nanofios, as cadeias atômicas lineares e mais atualmente o menor nanotubo de prata. Compostos por carbono também têm recebido grande atenção, como o grafeno. Assim a busca por novas estruturas com propriedades únicas tem se tornado incessante nas últimas décadas. Isso tem tornado cada vez mais importantes às ferramentas teóricas, uma vez que elas podem tanto ajudar na caracterização de novas estruturas, como também as prever, como poderiam ser formadas, qual seria a sua geometria, quais condições seriam necessárias para a sua formação ou demais características eletrônicas. Neste contexto, apresentamos nesta tese, o estudo destas novas nanoestruturas iniciando pelos fatores que influenciam na formação de cadeias atômicas lineares cm nanofios de platina e como a temperatura pode ser essencial para a presença de distâncias anômalas em nanofios de ouro. Cálculos de transporte também foram efetuados para nanofios de ouro e prata, com o fim de correlacionar possíveis geometrias encontradas em experimentos de HRTEM com os perfis de condutância obtidos em experimentos MCBJ. Estudos da evolução do estiramento de nanofios de prata prosseguem com a análise da formação e transporte transporte do menor nanotubo de seção quadrada formada por prata. Formação e estrutura eletrônica de estrutura de carbono topologicamente idêntica a este tubo de prata foi também proposta. Por fim, estudamos as formações do grafano e do fluorografano, a partir da hidrogenação e fluoração de membranas de grafeno, respectivamente / Abstract: Nanotechnology had its symbolical beginning at the 1959\'s Nobel Prize awarder Richard Feynman\'s lecture: \"There is Plenty of Roam at the Bottom\". In this lecture, Feynman highlights the possibilities of creating new materials, designed to have specific electronic and structural properties. Ever since, great advances have been made and structures never dreamed before have been detected and synthesized. These are composed of very many different materials, from metals to carbon. As an example of metal made compounds, we have the nanowires, the linear atomic chains and more recently the smallest silver nanotube. Carbon made compounds have also received great attention; a great example is the graphene. This made the theoretical tools become increasingly important, since they can help both in the characterization of the new structures and in forecasting new ones, how could them be produced, what would its geometry be, which conditions would be necessary for its formation and the other electronic properties. ln this context, we present in this thesis the study of new nanostructures, beginning with the factors that influence in the atomic linear chains formation in platinum nanowires stretching and how the temperature can be essential to explain the presence of anomalous distances in gold nanowires. Transport calculations have also been made to gold and silver nanowires, in arder to correlate possible geometries found in HRTEM experiments with the conductance profiles obtained in MCBJ experiments. Studies in the stretch evolution of silver nanowires proceed with the analysis of formation and electronic transport in the smallest square section nanotube made of silver. Formation and electronic structure if a carbon topologically identical to this silver nanotube was also suggested. Lastly, we studied the formation of graphane and fluorographane respectively by the hydrogenation and fluorination of graphene membranes / Doutorado / Física / Doutor em Ciências

Malgré le mécanisme de base du transport protonique (PT) dans l'eau ait été proposé en 1806, à ce jour il n'existe pas de théorie complète qui décrive la protolyse. Ce phénomène est à la base du fonctionnement des batteries à hydrogène et de nombreux processus biologiques. Grâce à la technique de dynamique moléculaire Car-Parrinello (CPMD) et à l'aide de l'application d'un champ electrique (EF), une partie de cette thèse a été consacrée à l'étude du PT dans deux phase de la glace: la phase Ih et sa contrepartie ferroélectrique, la glace XI. Certains mécanismes ont été révélés: le rôle joué par les oxygènes lorsque se produit le PT et la contribution du (dés)ordre afin d'assister ce processus [1,2]. Le phénomène du PT est aussi à la base de nombreaux convertisseurs d'énergie constitués par le méthanol tels que le Direct Methanol Fuel Cells et les membranes Nafion. Afin de révéler la nature intime du PT dans le méthanol liquide, une série de simulations CPMD ont été menées sous l'effet d'un EF extérieur. De cette façon il a été possible de comparer le rôle joué par les liasons hydrogène afin d'assister le PT [3]. De plus, quand les intensités du champ sont plus élevées que celles qui donnent lieu au PT, certaines réactions chimiques ont été observées dans le même échantillon "numérique" du méthanol. En exploitant des paramètres typique de la "Théorie de la fonctionnelle de la densité conceptuelle", il a été possible de clarifier les conditions qui donnent lieu à ces réactions chimiques. Enfin, afin de quantifier la contribution du EF à la formation de méthane et de formaldéhyde dans le système, des simulations de métadynamique en conjonction à ceux ab initio ont été menées. / Although the basic mechanism of the proton transfer (PT) phenomenon in water has been envisaged in 1806, nowadays does not exist a detailed theoretical framework that envelop the protolysis process. This phenomenon is at the base of the operation of hydrogen batteries, as well as of many biological processes. Via the Car-Parrinello Molecular Dynamics (CPMD) technique and by means of the application of an electric field (EF), part of this thesis has been devoted to the detailed study of PT in two ice phases: ice Ih and its ferroelectric counterpart, ice XI. Several previously unknown mechanisms have been shown. As an example, the role played by the oxygens when a PT occurs and the contribution due to (dis)order in assisting this process [1,2]. The PT phenomenon is also at the base of the functioning of some methanol-based energy converters such as Nafion membranes. To the aim of disclosing the intimate nature of PT in liquid methanol, a series of CPMD simulations have been carried out by applying an external EF; the role played by the H-bond network have been also compared with the similar PT mechanism in water [3]. At field strengths higher than those leading to PT, several chemical reactions have been observed in this sample. By exploiting the conceptual Density Functional Theory framework, it has been possible to clarify the circumstances under which a given chemical reaction occurs. Moreover, in order to disclose the role played by the EF in assisting chemical reactions, the mechanism leading to the formation of formaldehyde and methane in the sample has been studied with metadynamics approaches in conjuction with the ab initio ones.

Dans cette thèse nous utilisons des méthodes globaux de prédiction des structures cristallographiques combinés à des techniques de grande capacité de traitement de données afin de prédire la structure cristalline de différents systèmes et dans des conditions thermodynamiques variées. Nous avons réalisé des prédictions structurales utilisant l'analyse cristalline par optimisation par essaims particuliers (CALYPSO) combinés avec la Théorie Fonctionnel de la Densité (DFT) ce qui a permis de mettre en évidence la stabilité de plusieurs composés jusqu'à la inconnus dans le digramme de phases du système Ba-Si et dans le système N-H-O. Nous avons également réalisé une étude à haute capacité de traitement de données sur un système ternaire de composition ABX2. Nous avons utilisé la Théorie Fonctionnel de la Densité combinant calculs de prototypes structuraux à partir des prédictions structurelles avec la méthode. Dans les paragraphes suivants nous résumons le contenu de différents chapitres de cette thèse. Le premier chapitre qui constitue une brève introduction au travail de cette thèse est suivi du chapitre 2 présentant les aspects théoriques utilisés dans ce travail. D'abord il est fait une brève introduction à la Théorie Fonctionnel de la Densité. A continuation nous décrivons quelques fonctions d'échange-corrélation choisies qui constituent des approximations rendant l'utilisation de la DFT efficace. Ensuite nous présentons différents procédés de prédiction structurale, et en particulier les algorithmes d'optimisation par essaims particuliers et de « Minima Hopping » qeu nous avons utilisés dans cette thèse. Finalement il est discuté comment doit-on se prendre pour évaluer la stabilité thermodynamique des nouvelles phases identifiées. Dans le chapitre 3, nous considérons le système Ba-Si. A travers l'utilisation d'une recherche structurale non-biaisée basée sur l'algorithme d'optimisation par essaims particuliers combinée avec des calculs DFT, nous faisons une étude systématique de la stabilité des phases et de la diversité structurale du système binaire Ba-Si sous haute pression. Le diagramme de phases résultant est assez complexe avec plusieurs compositions se stabilisant et se déstabilisant en fonction de la pression. En particulier, nous avons identifié des nouvelles phases de stœchiométrie BaSi, BaSi2, BaSi3 et BaSi5 qui devraient pouvoir être synthétisées expérimentalement dans un domaine de pressions étendu. Dans le chapitre 4 est présentée notre étude du diagramme de phases du système N-H-O. S'appuyant sur une recherche structural «évolutive » de type ab initio, nous prédisons deux nouvelles phases du système ternaire N-H-O qui sont NOH4 et HNO3 à de pressions allant jusqu'à 150 GPa. La nouvelle phase de NOH4 est stable entre 71 et 150 GPa, tandis que HNO3 est stable entre 39 et 150 GPa (la pression maximum de cette étude). Ces deux nouvelles phases sont lamellaires. Nous confirmons également que la composition NOH5 perd son stabilité pour des pressions supérieures à 122 GPa se décomposant en NH3 et H2O à cette pression. Le chapitre 5 se focalise sur les électrodes transparentes de type-p à base des chalcogénures ternaires. Nous utilisons une approche à grande capacité de traitement de données basée sur la DFT pour obtenir la delafossite et d'autres phases voisines de composition ABX2. Nous trouvons 79 systèmes qui sont absents de la base de données « Materials project database », qui sont stables du point de vue thermodynamique et qui cristallisent soit dans la structure delafossite, soit dans des structures très proches. Cette caractérisation révèle une grande diversité de propriétés allant depuis les métaux ordinaires aux métaux magnétiques et permettant d'identifier quelques candidats pour des électrodes transparents de type-p. Nous présentons enfin à la fin du manuscrit nos conclusions générales et les perspectives de ce travail / In this thesis we use global structural prediction methods (Particle Swarm Optimization and Minima Hopping Method) and high-throughput techniques to predict crystal structures of different systems under different conditions. We performed structural prediction by using the Crystal structure Analysis by Particle Swarm Optimization (CALYPSO) combined with Density Functional Theory (DFT) that made possible to unveil several stable compounds, so far unknown, on the phase diagrams of Ba-Si systerm and N-H-O system. Afterwards, we performed a high-throughput investigation on ternary compounds of composition ABX2, where A and B are elements of the periodic table up to Bi, and X is a chalcogen (O, S, Se, and Te) by using density functional theory and combining calculations of crystal prototypes with structural prediction (Minima Hopping Method). The following paragraphs summarize the content by chapter of this document. Chapter 1 is a short introduction of this thesis. Chapter 2 consists of the basic theory used in this thesis. Firstly, a short introduction of Density Function Theory (DFT) is presented. Then, we describe some approximate exchange- correlation functions that make DFT practical. Next, we introduce different structural prediction algorithms, especially Particle Swarm Optimization and Minima Hopping Method which we used in this thesis. Finally, we discuss the thermodynamic stablility criteria for a new a new structure. In Chapter 3, we first consider Ba–Si system. Using an unbiased structural search based on a particle-swarm optimization algorithm combined with DFT calculations, we investigate systematically the ground-state phase stability and structural diversity of Ba–Si binaries under high pressure. The phase diagram turns out to be quite intricate, with several compositions stabilizing/destabilizing as a function of pressure. In particular, we identify novel phases of BaSi, BaSi2, BaSi3, and BaSi5 that might be synthesizable experimentally over a wide range of pressures. Chapter 4 contains the investigation of the phases diagram of the N–H–O system. By using ab initio evolutionary structural search, we report the prediction of two novel phases of the N–H–O ternary system, namely NOH4 and HNO3 (nitric acid) at pressure up to 150 GPa. Our calculations show that the new C2/m phase of NOH4 is stable under a large range of pressure from 71 GPa to 150 GPa while the P21/m phase of HNO3 (nitric acid) is stable from 39 GPa to 150 GPa (the maximum pressure which we have studied). We also confirmed that the composition NOH5 (NH3H2O) becomes unstable for pressures above 122 GPa. It decomposes into NH3 and H2O at this pressure. Chapter 5 focuses on p-type transparent electrodes of ternary chalcogenides. We use a high-throughput approach based on DFT to find delafossite and related layered phases of composition ABX2, where A and B are elements of the periodic table, and X is a chalcogen (O, S, Se, and Te). From the 15 624 compounds studied in the trigonal delafossite prototype structure, 285 are within 50 meV/atom from the convex hull of stability. These compounds are further investigated using global structural prediction methods to obtain their lowest- energy crystal structure. We find 79 systems not present in the "Materials project database" that are thermodynamically stable and crystallize in the delafossite or in closely related structures. These novel phases are then characterized by calculating their band gaps and hole effective masses. This characterization unveils a large diversity of properties, ranging from normal metals, magnetic metals, and some candidate compounds for p-type transparent electrodes. At the end of the thesis, we give our general conclusion and an outlook

Recentemente um enorme esforço esta sendo feito na busca de bons materiais para aplicação na nova área emergente da eletrônica, a spintrônica. O estudo teórico tem se mostrado de fundamental importância em tal busca. Na presente dissertação estão alguns dos resultados de um estudo computacional envolvendo cálculos de primeiros princípios em Física dos Materiais. Utilizamos a ferramenta Vienna Ab-initio Simulation Package com suas implementações de funcionais de troca-correlação, para simular sistemas cristalinos de nitretos dos metais de transição (MT) vanádio (V), cromo (Cr), ferro (Fe) e cobalto (Co) na composição do tipo N-MT. Tomando como base a importância geral dos semicondutores existentes, escolhemos as estruturas zincblende(B3) e wurzita(B4), bem como a estrutura NaCl (B1) - esta ´ultima apenas para alguns cálculos do CrN. Determinamos teoricamente as constantes de rede de todos os materiais com a realização de minimizações completas das estruturas, relaxando os parâmetros geométricos. Tais resultados mostraram-se de ótima capacidade preditiva quando comparados com os valores experimentais. Sempre com o foco na spintrônica, estudamos diversas configurações magnéticas, e conseguimos com sucesso obter alguns materiais ferromagnéticos em seu estado fundamental. Seguindo a idéia de aplicação, estudamos o magnetismo dos diversos nitretos sob tensionamento hidrostático (expansão e compressão da célula), obtendo excelentes resultados, como o interessante caminho de transição magnética para o estado de meio-metal para os materiais na estrutura zincblende. Notadamente, as constantes el´asticas e bulk moduli de muitos materiais foram determinados - segundo os nossos conhecimentos, alguns deles pela primeira vez. Também realizamos um estudo inicial da estrutura eletrônica, com cálculos de densidades de estados e estruturas de bandas, tanto no estado fundamental, como sob tensionamento, e verificamos com sucesso a teoria de Stoner do magnetismo itinerante. Finalizamos o trabalho tocando no problema do tensionamento biaxial (planar), com o objetivo de estudar o magnetismo, a estrutura eletrônica e a estabilidade dos nitretos magnéticos, particularmente do CrN zincblende, no processo de crescimento epitaxial de filmes e heteroestruturas. / Recently a huge effort is been done to find good materials in order to aplied in a new eletronic area, spintronics.

Os compostos de fósforo apresentam várias implicações em processos atmosféricos e interestelares. Nesta tese, será realizado um estudo ab initio em três diferentes sistemas. (i) Um destes sistemas é o radical PCO. No capítulo três, foi analisado os aspectos conformacionais do radical PCO, sendo avaliado as propriedades moleculares e termodinâmicas da espécie cíclica e das espécies lineares. Entre os isômeros do radical PCO, a espécie i3 (C∞V, 2π) é a mais estável delas, com uma entalpia de formação a 0K de 22.33±2.10 kcal mol-1. Considerando as barreiras de energia, que convergem em direção a espécie i3, elas apresentam valores próximos de 10 kcal mol-1, ao passo que a energia necessária para a isomerização da molécula i3 para outros isômeros é acima de 60 kcal mol-1. Estes valores de energia explicam o fato que, em condições experimentais, foi detectado apenas a espécie i3 (C∞V, 2π). (ii) No capítulo quatro, foi elucidado o mecanismo da reação PH3 +F, assim como foi também caracterizado as propriedades eletrônicas dos intermediários observados nesta reação. Na reação PH3 +F, pode ser observado que, diferente da literatura, dois caminhos são possíveis para esta reação: (a) a reação de abstração de hidrogênio, com a formação dos produtos PH2 e HF, e a reação de adição-eliminação, com a formação das espécies PH2F e H. Analisando a energia eletrônica, é possível observar que a reação de adição-eliminação apresenta uma barreira de energia de 23 kcal mol-1 abaixo da mesma observada para a reação de abstração de hidrogênio. Considerando os intermediários formados na reação PH3 + F, são observados dois tipos de simetria: uma C1 e duas Cs. Além disso, a entalpia de formação em 298K dos intermediários variou de -22.99 to -29.74 kcal mol-1. (iii) No capítulo cinco, foi avaliada a interação da fosfina com diferentes aglomerados de água. Neste capítulo, foi realizada uma análise nos aglomerados PH3-(H2O)n (n=1-8,12,20) e avaliado a estabilidade dos potenciais isômeros, assim como as propriedades moleculares e espectroscópicas dos diferentes isômeros. Nas estruturas PH3-(H2O)n (n=1-8) foi possível observar que os modos vibracionais δ(PH3) e δsym(PH3) apresentaram um deslocamento para o vermelho, ao passo que as freqüências de estiramento simétrico e assimétrico da fosfina apresentaram um deslocamento para o azul. No caso da estrutura PH3(H2O)20, as variações nos modos vibracionais foram similares embora que mais intensas, sendo o mesmo também observado para as respectivas intensidades. Além disso, a energia necessária para o confinamento da fosfina no interior de um aglomerado de água dodecaedro hexagonal variou de -1.81 to -6.38 kcal mol-1. / The phosphorus compounds show several implications to atmospheric and interstellar processes. In this thesis, was performed an ab initio study on three different systems. (i) One of these systems is the PCO radical. In chapter three, was studied the conformation aspects of PCO radicals, which was assessed the molecular and thermodynamic properties of the cyclic and linear species. In PCO species, it was observed that the linear specie i3 (C∞V, 2π) is the most stable one, with the enthalpy formation at 0K of 22.33±2.10 kcal mol-1. Considering the barrier heights, which converge into the direction of i3, they are close to 10 kcal mol-1, while the energy necessary to the isomerization of i3 to other conformations are high than 60 kcal mol-1. These energy values explain the fact that, in experimental conditions, was detected only the i3 (C∞V, 2π) specie. (ii) In chapter four, it was elucidated the mechanism of the PH3 + F reaction, and it was also described the electronic properties of the intermediates observed in this reaction. In the PH3 + F reaction can be seen that, different from the literature, two possible pathways can be observed: (a) the hydrogen abstraction, with the formation of PH2 and HF products, (b) and the addition-elimination route, with the formation of PH2F and H species. Analyzing the electronic energy, can be observed that the barrier energy of the addition-elimination process is 23 kcal mol-1 bellow the hydrogen abstraction route. Considering the intermediates, two different point groups were detected: a C1 and two Cs. In addition, the enthalpy formation at 298K of the intermediates, in the PH3 + F reaction, range from -22.99 to -29.74 kcal mol-1. (iii) In chapter five, it was studied the interaction of phosphine with different water clusters. In this chapter was performed an analysis of the PH3-(H2O)n (n=1-8,12,20) clusters, and evaluated the stability of the potential isomers as also the molecular and spectroscopy aspects of the different species. In the PH3(H2O)n (n=1-8) structures are seen a redshift in the δ(PH3) and δsym(PH3) vibrational modes, while is observed a blueshift from the asymmetric and symmetric stretching frequencies of phosphine. In the case of PH3(H2O)20 structure, the variations in the vibrational modes were similar however more intense, as also in their respective intensities. In addition, the necessary energy to trap phosphine in the interior of an hexagonal dodecahedron water clusters range from -1.81 to -6.38 kcal mol-1.

Au cours de son cycle de vie, le principe actif se retrouve en solution dans différentes situations : dans desformes pharmaceutiques liquides, dans l’organisme et dans les eaux usées. Or, par rapport à l’état solide, lamise en solution du principe actif l’expose davantage à des facteurs susceptibles de conduire à sa dégradation.Les transformations modifient sa structure chimique et donc potentiellement ses activités pharmacologiques ettoxicologiques.L’objectif de ce travail de thèse est de présenter une méthodologie et des études visant à prédire le devenir ensolution de principes actifs et les impacts potentiels consécutifs à leur dégradation.Trois principes actifs ont été sélectionnés pour la réalisation de ce travail. Ils ont en commun de présenter,d’une part, une activité pharmacologique élevée corrélée à une toxicité potentielle de leurs produits dedégradation et, d’autre part, l'absence de données sur leurs comportements en solution. Dans tous les cas,bien que le contexte soit singulier pour chaque molécule, l’approche méthodologique suivie intègre aussi biendes travaux expérimentaux que des études ab initio et in silico.La première étude porte sur le devenir de l’apixaban, principe actif actuellement commercialisé sous formeorale solide, en solution aqueuse. Les données expérimentales ont mis en évidence des groupementschimiques du principe actif pouvant contribuer à son instabilité. L’approche ab initio a permis d’expliquer larégio-spécificité de la réaction d’hydrolyse dépendamment du pH. À partir de la structure des produits dedégradation caractérisés, l’étude de leur potentiel toxique a été réalisée par approche in silico. Ces donnéesconcourent à la démarche d'analyse et évaluation des risques déployée lors de développements de formespharmaceutiques liquides ou des situations particulières impliquant la mise en solution de l'apixaban aumoment de l'administration.De telles approches ont également été employées pour caractériser les mécanismes de photodégradation del’argatroban et évaluer le potentiel toxique des produits de dégradation. Les processus initiant laphotodégradation ont fait l’objet d’études complémentaires reposant sur des calculs d’énergies. Cesconnaissances pourront apporter le rationnel nécessaire au choix de procédés capables de réduire laphotodégradation de l’argatroban et son impact sur les patients. Elles pourront également servir à anticiper lessituations d’écarts pouvant mettre en jeu le rapport bénéfice risque du médicament telles que le mésusage oula modification de la forme pharmaceutique administrée.Enfin, dans un contexte autre que le contexte pharmaceutique, une étude de dégradation du pémétrexed parphotocatalyse via un procédé d'oxydation avancée a été réalisée. Il s'agit d'un procédé particulièrement étudiépour sa capacité à réduire l’empreinte environnementale de composés organiques en accélérant leurdégradation. Le choix de ce principe actif utilisé comme anticancéreux a été justifié par son caractère toxiqueet rémanent dans les eaux de surface, ce qui en fait un produit à haut risque environnemental. Ce travail amontré que des produits de plus faible masse résultant de la transformation photocatalytique du pémétrexedsont malheureusement plus toxiques et encore plus rémanents que la molécule mère elle-même. Ces résultatscontribuent donc à souligner que les procédés d'oxydation avancée, bien qu'efficaces pour l'élimination despolluants médicamenteux, sont à évaluer au regard de l'existence d'un risque accru pour l'environnementavant toute perspective d'utilisation à grande échelle.Les approches et les résultats présentés dans cette thèse pourront être employés pour d’autres études visant àprédire, prévenir et réduire l’impact de la dégradation du principe actif sur le patient et l’environnement. / During its life cycle, an active substance is in solution for various reasons: in a liquid pharmaceutical form, in the body and in wastewater. However, compared to the solid state, the active substance in solution exposes it more to factors likely to cause its degradation. The transformations modify its chemical structure and thus potentially its pharmacological and toxicological activities.The objective of this thesis is to present a methodology and studies aiming to predict the fate in solution of active substances and the potential impacts following their degradation.Three active ingredients have been selected for this work. They have in common, on the one hand, a high pharmacological activity correlated to a potential toxicity of their degradation products and, on the other hand, the fact that there is little information on their behaviour in solution. In all cases, although the context is specific to each molecule, the methodological approach followed integrates both experimental work and ab initio and in silico studies.The first study concerns the fate of apixaban, an active substance currently marketed in solid oral form, in aqueous solutions. The experimental data made it possible to highlight chemical groups of the active ingredient that could contribute to its own instability. The ab initio approach explained the regio-specificity of the hydrolysis reaction as a function of pH. Based on the structure of the characterized degradation products, their toxic potential was studied using an in silico approach. These data contribute to the risk analysis and evaluation process deployed at different stages of development of liquid pharmaceutical forms or in particular situations involving the solution of apixaban at the time of administration.Such approaches have also been used to characterize the photodegradation mechanisms of argatroban and assess the toxic potential of degradation products. The processes that initiate photodegradation were also addressed by calculating the energies potentially involved. This knowledge provides a rational basis for the choice of processes and formulations to limit photodegradation of argatroban and its impact on patients. They also make it possible to anticipate situations where the benefit/risk ratio of the medicinal product may be modified, such as incorrect handling or modification of the pharmaceutical form administered.Finally, in a context other than the pharmaceutical context, a study of degradation of pemetrexed by photocatalysis via an advanced oxidation process was carried out. This process is particularly studied for its ability to reduce the environmental footprint of organic compounds by accelerating their degradation. The choice of this active substance as an anti-cancer agent was justified by its toxic and persistent nature in surface waters, making it a product with a high environmental risk. This work has shown that products of lower mass produced by photocatalytic transformation of pemetrexed are unfortunately more toxic and even more persistent than the parent molecule itself. These results underline the fact that advanced oxidation processes, although effective in removing drug pollutants, must be evaluated because of an increased risk to the environment before any prospect of large-scale use.The approaches and results presented in this thesis can be used for other studies to predict, prevent and reduce the impact of active ingredient degradation on the patient and the environment.

Les molécules-aimants sont des complexes moléculaires contenant des ions des métaux de transition ou des lanthanides capables de présenter le phénomène de blocage de l’aimantation en dessous d’une température de blocage Tb. Ce blocage est dû à la présence d’une barrière d’énergie de réorientation de leur aimantation à cause de la présence d’une anisotropie magnétique uniaxiale qui conduit à la présence de deux états stables de l’aimantation.Ces deux états stables sont adressables avec un champ magnétique extérieur. Il est donc,théoriquement, envisageable d’utiliser ces molécules comme unités de base pour le stockage « classique » de l’information.Néanmoins, à cause de la nature quantique des molécules, une relaxation entre les deux états de l’aimantation a lieu à basse température par effet tunnel à travers la barrière d’énergie. Cet effet tunnel a plusieurs causes dont une correspondant à une légère déviation de l’anisotropie magnétique de la situation strictement axiale. Cet effet annule le caractère bistable (classique) des molécules les rendant inutilisables comme bits classiques pour le stockage de l’information. Mais, la présence de l’effet tunnel conduit à une situation particulière à basse température où deux niveaux sont présents séparés par une énergie liée au caractère non axiale (rhombique) de l’aimantation (cas où le spin est entier). Un système à deux niveaux est appelé bit quantique(qubit) et constitue l’unité de base pour la construction d’ordinateurs quantiques si plusieurs conditions sont réunies.Ainsi, pour concevoir des bits classiques ou quantiques, il est indispensable comprendre au niveau microscopique la nature de l’anisotropie magnétique et les facteurs qui l’influencent.Ce travail de thèse est consacré à l’étude théorique de la nature de l’anisotropie magnétique dans des complexes mononucléaires et binucléaires de Ni(II) (S = 1)et de Co(II) (S = 3/2). Des calculs de type ab initio, basés sur la théorie de la fonction d’onde,qui permettent d’extraire les paramètres de l’hamiltonien de spin de l’anisotropie magnétique ont été effectués. Des calculs sur des objets modèles et molécules réelles qui permettent de séparer l’effet des différents paramètres structuraux et électroniques des ligands sur la nature et l’amplitude de l’anisotropie magnétique ont aussi été réalisés.La comparaison entre les calculs sur des complexes modèles et sur des complexes réels permet de rationaliser les propriétés magnétiques des complexes réels et surtout de proposer des stratégies pour la synthèse de nouveaux complexes avec les propriétés souhaitées. L’étude de complexes binucléaires qui peuvent être considérés comme la première étape pour la conception de porte logique quantique a été réalisée. Les calculs sur les complexes binucléaires sont réalisés en fragmentant les molécules en deux espèces mononucléaires. Pour les complexes binucléaires de Ni(II) et Co(II), des calculs de type Density Functional Theory (DFT) pour évaluer l’amplitude et la nature de l’interaction d’échange ont été menés. Pour étudier l’influence d’une perturbation extérieure sur les propriétés magnétiques, l’influence d’un champ électrique placé parallèle et perpendiculaire à l’axe de facile aimantation d’un complexe de Ni(II) a été étudiée. Le champ électrique peut influencer les propriétés d’anisotropie de manière importante ouvrant la possibilité à la manipulation des molécules par cette perturbation. / Single molecule magnets are molecular complexes containing transition metal or lanthanides ions which are able to block their magnetization below a certain blocking temperature Tb. This blocking is caused by an energy barrier separating the two orientations of magnetization leading to two stable magnetization states. These two states can be controlled by an external magnetic field.Therefore, it is theoretically possible to use these molecules as bits which are able to store“classical” information. However, due to the quantum nature of these molecules, the relaxation of magnetization can exist even at low temperatures. This phenomenon is called the quantum tunneling effect and prevents the bistable (classical) behavior of the magnetic properties, as well as their use as classical bits for data strorage.Yet, the quantum tunneling of the magnetization also leads to a particular situation at a low temperature where two levels are separated by an energy related to the non-axial character(rhombic) of the magnetization (when the spinis an integer). Such two-levels system could be used as a quantum bit (qbit) which is the basic unit for quantum information processing. Thus,the design of classical or quantum bits require a precise understanding of magnetic properties and their origin at a microscopic level.The Ph.D work was devoted to the theoretical study of the magnetic anisotropy in mononuclear and binuclear Ni(II) (S=1) and Co(II) (S=3/2) complexes. Ab initio calculations based on the wave function theory were carried out and the spin Hamiltonian parameters were extracted. Model complexes were used to investigate the structural and electronic parameters causing magnetic anisotropy.Calculations were, also, performed on complexes synthesized in the laboratory.Comparison between real and model complexes allowed rationalizing the magnetic properties and imagining new synthesis strategies leading to the desired magnetic properties. Binuclear complexes that can be considered as double qbits and used to build quantum logic gates were also investigated. The calculations were performed by fragmenting the binuclear complexes into two mononuclear units in order to study the local anisotropy of each metal ion.The exchange interaction was investigated using Density Functional theory (DFT). In order to study the influence of an external perturbation on magnetic properties, the magnetic properties of a mononuclear Co(II) complex under an external electric field applied parallel or perpendicular to the axis of easy magnetization were calculated. The application of an electric field can lead to important modifications of magnetic properties. Thereby, offering the possibility to the manipulation of these molecules by external electric fields.

Le but de la thèse était de simuler le spectre d'absorption de méta-matériaux pour les applications photovoltaïques. Par méta-matériaux, nous entendons une assemblée d'objets de taille nanométrique situés à distance mésoscopique. L'idée sous-jacente est qu'en modifiant la taille du nano-objet et l'arrangement géométrique, on peut ajuster le seuil d'absorption. Pour calculer ces quantités, j'ai utilisé l'état de l'art du formalisme, c'est-à-dire des méthodes ab initio.La première étape du travail a été dédiée au calcul de l'absorption d'un objet isolé (tranche de silicium, graphène, hBN). Dans le cadre de codes périodiques, on utilise une supercellule avec du vide pour isoler l'objet, et une méthode a été développée précédemment dans le groupe de Spectroscopie Théorique du LSI, pour obtenir des résultats indépendants du vide. Elle est appelée Selected-G, et a été appliquée avec succès aux surfaces de silicium. Pour une tranche isolée, une expression modifiée du potentiel coulombien dans l'espace réciproque, appelé "slab potential", doit être utilisée. Pour valider l'utilisation du potentiel de slab pour le calcul de la matrice diélectrique microscopique, j'ai simulé les spectres de perte d'énergie d'électrons pour des empilements de quelques plans de graphène, et reproduit avec succès les données expérimentales disponibles. Cela a offert la possibilité d'étudier la dispersion du plasmon d'un plan de graphène, et discuter la nature des excitations électroniques dans ce système (transitions interband ou plasmon 2D).La second étape a été consacrée à l'étude du spectre d'absorption d'une assemblée de tranches en interaction. Comme il a été mis en évidence que le formalisme de supercellule agit comme une théorie de matériau moyen avec du vide, avec l'effet erroné d'avoir des spectres dépendant de la taille de la supercellule, j'ai renversé la procédure pour extraire le spectre de la tranche en interaction, affranchi du problème du vide. La faisabilité a été démontrée sur les tranches de hBN, dont le caractère semi-conducteur à large bande interdite évite les instabilités numériques.Cela a permis de comprendre la raison pour laquelle l'absorption de la tranche en interaction de silicium apparaît à plus basse énergie que celle du matériau massif: cela vient de la présence des états de surface dans la bande interdite de la structure de bandes du massif. Néanmoins, la différence avec la tranche isolée doit être encore étudiée.La troisième partie a été dédiée à l'étude de matériaux utilisés, ou candidats, aux applications photovoltaïques comme InP et InSe. J'ai étudié dans un premier temps les structures de bandes des massifs. Pour corriger la sous-estimation de la bande interdite calculée dans l'approximation de la densité locale (LDA), j'ai calculé les corrections GW, et utilisé la fonctionnelle d'échange et corrélation de Heyd-Scuseria-Ernzerhof (HSE). Le spectre d'absorption de InP massif a été calculé en résolvant l'équation de Bethe-Salpeter, qui permet de tenir compte des effets excitoniques. Comme ce calcul est très lourd numériquement, j'ai également comparé avec le calcul beaucoup plus léger de TDDFT avec le kernel à longue portée pour introduire les effets excitoniques. Pour le massif de InSe, j'ai calculé les corrections HSE pour les valeurs propres et obtenus un bon accord avec la bande interdite expérimentale. Les spectres obtenus en TDDFT, avec le kernel à longue portée, donne de bons résultats. J'ai commencé l'étude de tranches de ces deux matériaux. Des couches épaisses de InP et InSe ont été considérées et une reconstruction de surface (2x2) a été réalisée sur InP pour obtenir une surface semi-conductrice. La structure de bande LDA et les spectres d'absorption ont été calculés. Comme des systèmes d'une telle taille sont hors de portée des calculs de corrections HSE, l'étude s'est concentrés sur des tranches beaucoup plus fine de InSe. / The purpose of the thesis was to simulate the absorption spectrum of meta-materials for photovoltaic applications. By meta-material, we mean an assembly of nanometric size objects at mesoscopic distance. The underlying idea is that by adjusting the size of the nano-object and the geometric arrangement, one could tune the absorption edge. To calculate these quantities, I used state-of-the art formalism, namely ab-initio methods.The first step of the work has been dedicated to the calculation of the absorption of an isolated object (slab of silicon, graphene, hBN). In the framework of periodic codes, one uses a supercell with vacuum to isolate the object, and a method has been developed previously in the Theoretical spectroscopy group at LSI, to provide results independent of vacuum. It is called “Selectd-G” method, and was successfully applied to silicon surfaces. For an isolated slab, a modified expression of the reciprocal space Coulomb potential, called “slab potential”, must be used. To validate the use of the slab potential on the microscopic dielectric matrix, I have simulated Electron Energy Loss spectra for slabs of few graphene layers, and successfully reproduced available experimental data. This has also offered the possibility to study the plasmon dispersion of a single graphene layer, and discuss the nature of electronic excitations in the system (intraband transitions or 2D-plasmon).The second step has been dedicated to the study of the absorption spectrum of an array of interacting slabs. Since it has been evidenced that the supercell formalism acts as an effective medium theory with vacuum, with the spurious effect of having spectra dependent on the size of the supercell, I have reversed the procedure to extract the spectrum of the interacting slab, "cured" from the vacuum problem. First, the feasibility has been demonstrated on slabs of hBN, as their semi-conducting characteristics with a the large gap prevent numerical instabilities. Then, it has allowed us to understand the reason why the absorption of the interacting slab of silicon appears at lower energy than its bulk counterpart: it is due to the presence of surface states in the gap of the bulk band structure. Nevertheless, the difference with the isolated slab must be further investigated.The third part has been dedicated to the study of materials currently used or candidates for photovoltaic applications: InP and InSe. I have first studied the band structures of bulk InP and InSe. To correct for the underestimation of the band gap in the local density approximation (LDA), I have used GW corrections and the Heyd-Scuseria-Ernzerhof (HSE) exchange-correlation functional. The absorption spectrum for bulk InP has been calculated by means of the solution of the Bethe-Salpeter equation to correctly account for the excitonic effects. As expected, the experimental macroscopic function is well reproduced. Since the calculation is numerically demanding, I have also compared the results with the much lighter calculation using TDDFT where I used the long range kernel to mimic the excitonic effects. For bulk InSe, I have calculated the HSE corrections for the eigenvalues and obtained a good agreement with the experimental band gap. The spectrum obtained within TDDFT, with the long range kernel, gives satisfying results. We have started the calculations for slabs of these two materials. Thick slabs of InP and InSe have been considered and a 2x2 reconstruction have been performed for the InP slab to recover the semi-conducting surface. The LDA band structures and absorption spectra have been calculated. Then, such large systems being out of range of HSE corrections calculations, the study has been focused on much thiner slabs in the case of InSe.

Ce travail a consisté à étudier des complexes de Fer (II) et plus particulièrement à décrire le phénoméne de piégeage d'états de spin excités par la lumière. La taille des molécules présentant cette propriété étant d'une centaine d'atomes, la théorie de la fonctionnelle de la densité (DFT) à été la méthode de choix. Au travers de cette étude, les limites d'application de la DFT aux complexes de Fer (II) ont été évaluées en les comparant à des calculs ab initio puis à des données expérimentales. Il a été mis en évidence que le terme d'échange des fonctionnelles l'échange-corrélation influence le plus la capacité à décrire Delta E_{HL} et Delta r_{HL}. La fonctionnelle OLYP de type GGA a permis d'obtenir la meilleure description de ces complexes. Les énergies à décrire étant de l'ordre de la précision chimique (kcal/mol), les fonctionnelles d'échange doivent être encore améliorées pour obtenir des résultats plus fiables.