Orientadora: Paula Homem de Mello / Disseração (mestrado) - Universidade Federal do ABC. Programa de Pós-Graduação em Ciência eTecnologia/Química, 2012

Orientadora: Profa. Dra. Káthia Maria Honório / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Ciência & Tecnologia - Química, 2014. / Polimeros de impressao molecular (MIPs) sao materiais sinteticos que possuem sitios de reconhecimento molecular especificos para determinado analito de interesse (molecula molde), e tem sido empregados para a pre-concentracao e extracao em amostras complexas, considerando a maior seletividade em relacao aos sorventes convencionais empregados na extracao em fase solida. A escolha dos reagentes utilizados na sintese de um MIP deve ser criteriosa, a fim de que sejam criados sitios de ligacoes especificos. Metodos computacionais de Quimica Teorica podem ser empregados para racionalizar o planejamento de MIPs, por intermedio do estudo de parametros fisico-quimicos das moleculas envolvidas e as interacoes que ocorrem no sistema de pre-polimerizacao. Com a utilizacao de metodos de quimica quantica, foi objetivo desse trabalho o estudo previo das interacoes entre as moleculas moldes e os possiveis reagentes empregados na sintese de MIPs, como forma de predicao das melhores interacoes que promovam um MIP de desempenho ideal. O estudo teorico foi direcionado para a molecula de ¿¢9-tetrahidrocanabinol (¿¢9-THC), substancia presente na planta Cannabis sativa e que e a substancia ilicita mais produzida e consumida mundialmente, e seu principal metabolito de excrecao urinario, o 11-nor-9-carboxi-¿¢9-THC (THC-COOH). A simulacao computacional foi realizada utilizando a Teoria do Funcional da Densidade (DFT), e a metodologia envolveu a comparacao das energias de interacao (¿¢E) dos adutos de pre-polimerizacao entre a molecula molde e os reagentes de sintese. Com os resultados das simulacoes, verificou-se que as melhores interacoes ocorrem quando o monomero utilizado tem caracteristica acida, como o acido acrilico e o acido metacrilico; e que o solvente mais adequado para a sintese sao os que apresentam baixa constante dieletrica, como o cloroformio e o tolueno, por interferirem menos na formacao do complexo de interacao entre a molecula molde e o monomero na etapa de pre-polimerizacao. Detalhes das interacoes existentes entre as moleculas do meio reacional tambem foram analisadas e forneceram informacoes sobre a possivel competicao entre as moleculas no acesso aos sitios de interacao das moleculas moldes, informacao crucial para obtencao de MIPs seletivos e de grande afinidade a molecula molde desejada. A partir das predicoes do estudo computacional, os MIPs de THC-COOH foram sintetizados com os monomeros indicados, juntamente com o polimero nao impresso (NIP), em alguns dos solventes simulados (agua, acetonitrila, metanol e agua), para avaliacao da interferencia do solvente na eficiencia do MIP obtido. Foi realizada a analise dos MIPs por espectroscopia vibracional na regiao do infravermelho, e avaliada as bandas de absorcao nas regioes dos grupos C=O e O-H, para analise da formacao de interacoes por ligacao de hidrogenio. Concluiu-se, portanto, que sem substituir os ensaios experimentais, a abordagem computacional pode ser utilizada como uma ferramenta preliminar e complementar a selecao experimental. / Molecularly imprinted polymers (MIPs) are synthetic materials with specific sites of molecular recognition for a given analyte of interest (template molecule), and have been used for the extraction and pre-concentration in complex samples, considering the higher selectivity presented in relation to the sorbent employed in conventional solid phase extraction. The choice of the reagents used in the synthesis of a MIP must be chosen carefully, so that site-specific linkages are created. Computational methods in Theoretical Chemistry can be used to rationalize the planning of MIPs through the study of physico-chemical parameters of the molecules involved and the interactions that occur in the pre-polymerization system. Using quantum chemical methods, the aim of this study was a preliminary investigation of the interactions between the template molecules and the possible reagents used in the synthesis of MIPs, as a way to predict the best interactions that promote MIPs with optimal performance. The theoretical study was directed to the molecule of Ä9-tetrahydrocannabinol (Ä9-THC), present in the plant Cannabis sativa, and that is the illicit substance most widely produced and consumed globally, as well as its major metabolite urinary excretion, 11 -nor-9-carboxy-Ä9-THC (THC-COOH). The computational simulation was performed using the Density Functional Theory (DFT), and the methodology involved the comparison of the interaction energies (ÄE) of adducts in pre-polymerization between the template molecule and reagents for synthesis. From the results of the simulations, it was found that the best interactions occur when the monomer has acid characteristic, such as acrylic acid and methacrylic acid; and that the most suitable solvent for synthesis are those with low dielectric constant such as toluene and chloroform, by interfering less in the formation of complex interaction between the template molecule and monomer in the pre-polymerization step. Details of the existing interactions between the molecules of the reactional medium were analyzed and provided information about the possible competition between the molecules in the access to the interaction sites of the template molecules, which is a crucial information for obtaining selective MIPs and with high affinity to the template molecule desired. From the computational predictions obtainde in this study, the MIPs of THC-COOH was synthesized with the indicated monomers, and also a non-imprinted polymer (NIP), considering some of simulated solvents (water, acetonitrile, methanol and water) for evaluation of the interference of solvent in the efficiency of the MIP obtained. Analyses on the formed MIPs were performed by spectroscopy in the infrared region, and the absorption bands in the regions of the groups C=O and OH were evaluated with the aim of analysing the formation of hydrogen bond interactions. Therefore, it is possible to conclude that, without replacing the experimental trials, the computational approach can be used as a preliminary and complementary tool to experimental selection.

Nesta dissertação, estudamos cadeias unidimensionais antiferromagnéticas de spins 1/2 modeladas pelo Hamiltoniano de Heisenberg na presença de inomogeneidades causadas principalmente pela introdução de ligações substitucionais (defeitos nas ligações) e por efeitos de borda. Interessados então em determinar a energia do estado fundamental de sistemas com quaisquer distribuições das ligações, utilizamos o formalismo da Teoria do Funcional da Densidade (DFT) desenvolvido para o modelo de Heisenberg. O formalismo da DFT permite a estimativa da energia do estado fundamental de sistemas não-homogêneos conhecendo-se o sistema homogêneo. Construímos funcionais na aproximação da ligação local (LBA), proposta recentemente em analogia à já conhecida LSA (aproximação local para o spin). A obtenção dos funcionais se baseou no estudo do modelo de uma cadeia de spins em que as ligações são alternadas, isto é, a interação de troca se alterna em valor de sítio para sítio. Isso originou um funcional não-local na interação de troca da cadeia. Apesar disso, continuamos utilizando a nomenclatura LBA. Todos os resultados fornecidos pelos funcionais são comparados a dados provenientes de diagonalização numérica exata. / In this dissertation, we use the Heisenberg model to describe inhomogeneous antiferromagnetic spin 1/2 chains. The translational invariance is broken mainly due to the non-uniform distribution of bond interactions (defects) and the presence of boundaries. Interested in obtaining the ground-state energy of systems with any distribution of exchange couplings (Jij), we use the density-functional theory (DFT) formalism, developed for the Heisenberg model. The DFT formalism allows an estimate of the ground-state energy of inhomogeneous systems based on the homogeneous systems. We build functionals for the ground-state energy using a local bond approximation (LBA), recently proposed in analogy to the already known LSA (local spin approximation). To obtain the functionals we studied a model that describes an alternating chain, in which the exchange coupling alternates from site-to-site. This resulted in non-local functionals on the spin-spin exchange interaction. Nevertheless, we still call them LBA functionals. All the results from the functionals are compared with exact numerical data.

O efeito Hall quântico surge em gases de elétrons bidimensionais (2DEG) na presença de altos campos magnéticos B. O campo magnético quantiza o movimento planar dos elétrons em órbitas ciclotrônicas caracterizadas pelos níveis de Landau. Neste regime a resistividade transversal (ou Hall) ρxy em função de B exibe platôs em submúltiplos inteiros de e2/h, i.e., ρxy = ν-1 e2/h, sendo ν o fator de preenchimento dos níveis de Landau. Por sua vez, a resistividade longitudinal ρxx apresenta picos nas transições entre platôs de ρxy. Em primeira instância, ρxx é uma medida indireta da densidade de estados no nível de Fermi g(εF), e os picos dos mesmos indicam cruzamentos do nível de Fermi εF com niveis de Landau. Assim, o diagrama de densidade de elétrons n2D e B dos picos de ρxx ~ g(εF) fornece um mapa topológico da estrutura eletrônica do sistema. Em sistemas de duas subbandas, ρxx(n2D, B) exibe estruturas em forma de anel devido a cruzamentos de níveis de Landau de subbandas distintas [experimentos do grupo do Prof. Jiang (UCLA)]. Estes cruzamentos podem ainda levar a instabilidades ferromagnéticas. Investigamos estas instabilidades usando a teoria do funcional da densidade (DFT) para o cálculo da estrutura eletrônica, e o modelo de Ando (formalismo de Kubo) para o cálculo de ρxx e ρxy. Para temperaturas mais altas (340 mK) obtemos as estruturas em forma de anel em ρxx. Para temperaturas mais baixas (70 mK), observamos uma quebra dos anéis devido a transições de fase ferromagnéticas. Variando-se o ângulo θ de B com relação ao 2DEG observa-se o encolhimento do anel. Nossos resultados mostram que o ângulo de colapso total do anel depende de uma competição entre o termo de troca da interação de Coulomb (princípio de Pauli) e cruzamentos evitados devido ao ângulo θ finito. As transições de fase exibem ainda o fenômeno de histerese. Na região de instabilidade ferromagnética obtemos diferentes soluções variando B de forma crescente ou decrescente. Estas soluções possuem energias total diferentes, de forma que representam estados fundamental e excitado de muitos corpos. Esta observação, juntamente com resultados anteriores do grupo [Freire & Egues (2007)], representam as primeiras realizações teóricas da previsão da possibilidade de estados excitados como mínimos locais do funcional de energia do estado fundamental [Perdew & Levy (1985)]. O modelo aqui proposto fornece excelente acordo com os experimentos considerados. Adicionalmente, a observação sistemática e experimentalmente verificada dos estados excitados valida as previsões de Perdew & Levy. Aplicamos ainda estas mesmas ideias no cálculo da estrutura eletrônica e condutância de fios quânticos na presença de campos magnéticos, mostrando que cruzamentos de modos transversais também exibem instabilidades ferromagnéticas observadas em experimentos recentes [Dissertação de Mestrado de Filipe Sammarco, IFSC/USP], fortalecendo a validade do modelo apresentado nesta tese. / The quantum Hall effect arises in two dimensional electron gases (2DEG) under high magnetic fields B. The magnetic field quantizes the planar motion of the electrons into cyclotron orbits given by the Landau levels. In this regime the transversal (Hall) resistivity ρxy shows plateaus as a function of B at integer sub-multiples of e2/h, i.e., ρxy = ν-1 e2/h, where n is the filling factor of the Landau levels. The longitudinal resistivity ρxx shows peaks at the transition between the plateaus of ρxy. In principle, ρxx is an indirect measure of the density of states at the Fermi level g(εF), so that the peaks indicate when the Fermi level εF crosses a Landau level. Therefore, a density-B-field diagram n2D-B of the ρxx ~ g(εF) peaks shows a topological map of the electronic structure of the system. In two-subband systems, ρxx( n2D, B) shows ringlike structures due to crossings of spin-split Landau levels from distinct subbands [experiments from the group of Prof. Jiang (UCLA)] that could lead to ferromagnetic instabilities. We study these instabilities using the density functional theory (DFT) to calculate the electronic structure, and Ando\'s model (Kubo formalism) for ρxx and ρxy. At higher temperatures (340 mK) we also obtain the ringlike structures in ρxx. At lower temperatures (70 mK) we see broken rings due to quantum Hall ferromagnetic phase transitions. Tilting B by theta with respect to the 2DEG normal we find that the ring structure shrinks. Our results show that the angle of full collapse depends on a competition between the exchange term from the Coulomb interaction (Pauli principle) and the anticrossing of Landau levels due to the finite angle theta. Additionally, at the instabilities we observe hysteresis. Sweeping the B field up or down near these regions we obtain two different solutions with distinct total energies, corresponding to the ground state and an excited state of the many-body system. This result, together with previous results of our group [Freire & Egues (2007)], are the first realizations of the theoretical prediction of the possibility of excited states as local minima of the ground state energy functional [Perdew & Levy (1985)]. The model proposed here shows an excellent agreement with the experiments. Additionally, the systematic and experimentally verified observation of excited states corroborates the predictions of Perdew & Levy. Similar ideas as presented here when applied to the electronic structure and conductance of quantum wires with an in-plane magnetic field show ferromagnetic instabilities at crossings of the wire transverse modes [Master Thesis of Filipe Sammarco, IFSC/USP], also with excellent experimental agreement. This strengthen the range of validity of the model proposed in this Thesis.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / O grafeno à atualmente o tÃpico mais corrente em fÃsica da materia condensada e ciÃncia dos materiais e foi isolado pela primeira vez a menos de quatro anos. O grafeno tem sido proposto como um material alternativo aos nanotubos de carbono em diversas aplicaÃÃes, devido a sua fÃcil sintetizaÃÃo e seu baixo custo. A fim de explorar uma potencial aplicaÃÃo dessas nanoestruturas em dispositivos eletrÃnicos, atravÃs de cÃlculos de primeiros princÃpios baseados na teoria do funcional da densidade, estudamos a interaÃÃo entre uma superfÃcie de grafeno e Ãtomos alcalinos (Li, Na e K) e halogÃnios (Cl, I e I2). Verificamos que a adsorÃÃo desses Ãtomos na superfÃcie do grafeno provoca significativas modificaÃÃes na estrutura eletrÃnica do grafeno. Observamos uma grande transferÃncia de carga entre os Ãtomos alcalinos (halogÃnios) e a superfÃcie do grafeno. Essas transferÃncias foram da ordem de 0,65-0,85 e- dos Ãtomos alcalinos para o grafeno e 0,37 (0,27) e- do grafeno para o Ãtomo de cloro (iodo). Os metais alcalinos apresentaram uma maior estabilidade sobre o centro de um hexÃgono do grafeno, tendo energias de ligaÃÃo entre -1,47 e -1,03 eV, onde a ordem de intensidade à dada por Li > K > Na. Essa predisposiÃÃo por um sÃtio especÃfico nÃo foi observada para os dois halogÃnios estudados. O Ãtomo de cloro apresentou uma maior estabilidade quando adsorvido sobre um Ãtomo da superfÃcie do grafeno, com energia de ligaÃÃo da ordem de 0,98 eV, no entanto, isso nÃo foi visto no caso do Ãtomo de iodo onde energias de ligaÃÃo equivalentes para todos os sÃtios estudados foram encontradas da ordem de 0,42 eV. A molÃcula I2 tambÃm nÃo apresentou uma predileÃÃo por uma sitio especÃfico da superfÃcie do grafeno, mas mostrou-se mais estÃvel quando adsorvida com seu eixo perpendicular ao plano do grafeno. / Graphene is currently the hottest topic in condensed-matter physics and materials science and was isolated less than four years ago. Graphene layers have been proposed as alternative materials for replacing carbon nanotubes in some applications, due to its easy synthesis and low costs. In order to explore potential applications of those nanostructures in electronic devices, through first principles based on the density functional theory, we studied the interaction between graphene surface and alkaline (Li, Na and K) and halogens (Cl, I and I$_2$ ) atoms. We verified that the adsorption of these atoms on the graphene surface cause significant modifications in the graphene electronic structure. We observed a large charge transfer between the alkaline (halogens) atoms and graphene surface. These charge transfers were found to be 0,65 - 0,85 e- from the alkaline atoms to graphene and 0,37 (0,27) e- from the graphene to chlorine (iodine) atoms. The alkaline atoms presented a larger stability on the center of one of the graphene hexagons, presenting binding energy in the range -1, 47 and -1, 03 eV, where the order of intensity is given by Li > K > Na. This predisposition for a specific site was not observed for the twostudied halogens. The chlorine atom present the larger stability when adsorbed on a top atom of the graphene surface with binding energy about 0, 98 eV, however this behavior was not be seen in the iodine atom case where equivalent binding energies for all the studied sites were found to be about 0,42 eV. The I2 molecule also does not present predilection for a specific site on the graphene surface, however it showed more stable when adsorbed with its axis perpendicular to the graphene surface plane.

Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-12-05T17:42:30Z No. of bitstreams: 1 StanrleyBandeira.pdf: 1297237 bytes, checksum: c39acc4db03b1190e402e8b3a4c9d8ff (MD5) / Made available in DSpace on 2017-12-05T17:42:30Z (GMT). No. of bitstreams: 1 StanrleyBandeira.pdf: 1297237 bytes, checksum: c39acc4db03b1190e402e8b3a4c9d8ff (MD5) Previous issue date: 2017-08-28 / FAPEMA / The present master's work was focused on quantum chemistry calculations and based on the Functional Density Theory (DFT) the interaction between platinum compounds used in anti-cancer therapy and DNA. Based on the analysis of the factors that influence the bonding process between the platinum complexes and the DNA. All the nitrogenous bases of the DNA were analyzed, in order to choose the one that would present better interaction with the studied complexes. The theoretical results showed that the different platinum compounds have binders that decrease toxicity, or increase membrane binding. The platinum compounds, Carboplatin, Iproplatin, Nedaplatin and Oxaliplatin, were structured through the GAUSS VIEW 5.0 software. Then, the optimization of these structures was performed using the GAUSSIAN 9.0 program. This optimization used bases extracted from the EMSL BASIS SET EXCHANGE database. As a result of these optimizations the HOMO-LUMO intervals were used to characterize the stability of the molecules, as well as the stability variations that occurred during the hydrolysis reactions, and their connections with the guanine base of the DNA. This observation, as well as the thermodynamic properties, served to describe the toxicities presented in the literature. / O presente trabalho de mestrado foi voltado a examinar por meio de cálculos de química quântica e com base na Teoria do Funcional Densidade (DFT) a interação entre compostos de platina usados na terapia anti-câncer e o DNA. Com base na análise dos fatores que influenciam o processo de ligação entre os complexos de platina e o DNA.Analisou-se todas as bases nitrogenadas do DNA, para a escolha da que apresentaria melhor facilidade de interação com os complexos estudados. os resultados teóricos mostraram que que os diferentes compostos de platina apresentam ligantes que diminuem a toxicidade, ou aumentam a ligação com membranas. Os compostos platínicos,Carboplatina, Iproplatina, Nedaplatina e Oxaliplatina, foram estruturados através do progarama GAUSS VIEW 5.0. Em seguida realizou-se a otimização dessas estruturas utilizando-se o programa GAUSSIAN 9.0. Essa otimização utilizou bases extraídas do banco de dados EMSL BASIS SET EXCHANGE. Como resultado dessas otimizações foram extraídos os intervalos HOMO-LUMO, utilizados para caracterizar a estabilidade das moléculas, bem como, as variações de estabilidade, que ocorriam durante as reações de hidrolise, e respectivas ligações com a base GUANINA do DNA. Essa observação,bem como as propriedades termodinâmicas serviu para descrever as toxicidades, apresentadas em literatura.

abstract: Attaining a sufficiently large critical current density (Jc) in magnetic-barrier Josephson junctions has been one of the greatest challenges to the development of dense low-power superconductor memories. Many experimentalists have used various combinations of superconductor (S) and ferromagnetic (F) materials, with limited success towards the goal of attaining a useful Jc. This trial-and-error process is expensive and time consuming. An improvement in the fundamental understanding of transport through the ferromagnetic layers and across the superconductor-ferromagnetic interface could potentially give fast, accurate predictions of the transport properties in devices and help guide the experimental studies. In this thesis, parameters calculated using density functional methods are used to model transport across Nb/0.8 nm Fe/Nb/Nb and Nb/3.8 nm Ni /Nb/Nb Josephson junctions. The model simulates the following transport processes using realistic parameters from density functional theory within the generalized gradient approximation: (a) For the first electron of the Cooper pair in the superconductor to cross the interface- conservation of energy and crystal momentum parallel to the interface (kll). (b) For the second electron to be transmitted coherently- satisfying the Andreev reflection interfacial boundary conditions and crossing within a coherence time, (c) For transmission of the coherent pair through the ferromagnetic layer- the influence of the exchange field on the electrons’ wavefunction and (d) For transport through the bulk and across the interfaces- the role of pair-breaking from spin-flip scattering of the electrons. Our model shows the utility of using realistic electronic-structure band properties of the materials used, rather the mean-field exchange energy and empirical bulk and interfacial material parameters used by earlier workers. [Kontos et al. Phys. Rev Lett, 93(13), 137001. (2004); Demler et al. Phys. Rev. B, 55(22), 15174. (1997)]. The critical current densities obtained from out model for Nb/0.8 nm Fe/Nb is 104 A/cm2 and for Nb/3.8 nm Ni/Nb is 7.1*104 A/cm2. These values fall very close to those observed experimentally- i.e. for Nb/0.8 nm Fe/Nb is 8*103 A/cm2 [Robinson et al" Phys. Rev. B 76, no. 9, 094522. (2007)] and for Nb/3.8 nm of Ni/Nb is 3*104 A/cm2 [Blum et al Physical review letters 89, no. 18, 187004. (2002). This indicates that our approach could potentially be useful in optimizing the properties of ferromagnetic-barrier structures for use in low-energy superconducting memories. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2018

Guanine is generally accepted as the most easily oxidized DNA base when cells are subjected to ionizing radiation, photoionization or photosensitization. At pH 7, the midpoint reduction potential is on the order of 0.2 – 0.3 V higher than those of the radicals of e.g. tyrosine, tryptophan cysteine and histidine, so that the radical “repair” (or at least, a thermodynamically favorable reaction) involving these amino acids is feasible. Computational quantum studies have been done on tyrosine, tryptophan, cysteine and histidine side chains as they appear in histones. Density functional theory was employed using B3LYP/6-31G+ (d, p) basis set to study spin densities on these amino acids side chains as they pair with the guanine radical cation. The amino acid side chains are positioned so as not to disrupt the Watson-Crick base pairing. Our results indicate that, these side chains of amino acid with reducing properties can repair guanine radical cation through electron transfer coupled with proton transfer.

Molecular modeling, using both ab initio and semi-empirical methods has been undertaken for a series of dirhodium complexes in order to improve the understanding of the nature of the chemical bonding in this class of homogeneous catalysts. These complexes, with carboxylamidate and carboxylate ligands, are extremely functional metal catalysts used in the synthesis of pharmaceuticals and agrochemicals. The X-ray crystallography shows anomalies in the bond angles that have potential impact on understanding the catalysis. To resolve these issues, minimum energy structures of several examples (e.g. Rh2(NHCOCH3)4, Rh2(NHCOCH3)4NC, Rh2(CO2CH3)4, Rh2(CO2CH3)4NC, Rh2(CHO2)4, and Rh2(CHO2)4NC) were calculated using Hatree-Fock and Density Functional Theory/B3LYP with the LANL2DZ ECP (Rh), and cc-pVDZ (all other atoms) basis sets.

Dans un superréseau, le confinement modifie les états électroniques et la réduction de symétrie produit une forte anisotropie des propriétés optiques. Dans les super-réseaux GaAs/AlAs cette anisotropie, avec en plus les effets non-linéaires dans les propriétés optiques de GaAs, est un élément essentiel pour la réalisation des convertisseurs de fréquence. Dans mon travail de thèse, j'ai étudié le tenseur diélectrique statique et les spectres d'absorption des superréseaux (GaAs)p/(AlAs)p en fonction de leur période p. Le calcul de ces quantités a été commencé à l'aide de techniques semi-empiriques à l'Université de Pavia, sous la direction du Prof. L.C. Andreani. En particulier, J'ai développé un code pour appliquer la méthode «linear combination of bulk bands» au calcul des structures de bande et des fonctions diélectriques des héterostructures (superréseaux et nanofils). Dans la suite j'ai passé 12 mois au LSI sous la direction du Dr. Lucia Reining, pour réaliser des calculs ab-initio dans le cadre de la théorie de la fonctionnelle de la densité dépendante du temps. Nous avons réussi à bien décrire l'effet du confinement sur les spectres. L'anisotropie de la réponse diélectrique, mesurée par la biréfringence, est déterminée par les contributions du confinement et des champs locaux cristallins : si on tient compte des deux effets, on peut reproduire les données expérimentales. Les ultérieurs effets à N-corps ne donnent que des corrections quantitatives. La comparaison entre les résultats des calculs ab-initio et semi-empiriques, ainsi qu'avec les données de l'expérience, nous a permis de détecter les mécanismes physiques essentiels qui contribuent à l'anisotropie des propriétés optiques et, de plus, de déterminer les limites de validité de la méthode semi-empirique et de l'approche classique des milieux effectifs.