Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-06-02T20:09:54Z No. of bitstreams: 1 LeidianaSousaLima.pdf: 1258368 bytes, checksum: 012183297e9fc650daa7de037cb6a95b (MD5) / Made available in DSpace on 2017-06-02T20:09:54Z (GMT). No. of bitstreams: 1 LeidianaSousaLima.pdf: 1258368 bytes, checksum: 012183297e9fc650daa7de037cb6a95b (MD5) Previous issue date: 2016-09-02 / Fundação de Amparo à Pesquisa e ao Desenvolvimento Científico e Tecnológico do Maranhão (FAPEMA) / This paper presents the results obtained by quantum study applying the functional theory of density - DFT and using the B3LYP functional to verify the electronic structures of Tetraazamacrociclos Cobalt (CoN4) and their interactions with oxygen through Griffith adsorption models (Side-on) and Pauling (End-on). The initial structures of Porphyrin Cobalt complex – CoP, Octametilporfirina Cobalt - CoOMP, Tetrametilporfirina Cobalt - CoTMP, tetraaza [14] annulene Cobalt - CoTAA and Dibenzotetraaza [14] annulene Cobalt - CoDBTAA were obtained from GaussView program and optimization the geometry and charge distribution of the structures, as well as their interactions with molecular oxygen were carried out using the Gaussian 09 program. The results shows that the structure of the macrocycle ligands influence O2 binding capacity to cobalt. In evaluating the interaction with oxygen, porphyrin cobalt and its derivatives showed better evidence against group tetraaza [14] annulene, for interaction with molecular oxygen due to weakening of the bond in the O2 molecule characteristic enhanced by data from Mulliken charge. Therefore, the order of interaction presented by the studied complexes is CoTMP, CoOMP, CoP, CoDBTAA and CoTAA in End-on model and CoP CoOMP, CoTMP, CoDBTAA and CoTAA in side-on model. / Este trabalho apresenta os resultados obtidos por meio estudo quântico aplicando a Teoria do Funcional da Densidade – DFT e usando o funcional B3LYP para verificar as estruturas eletrônicas de Tetraazamacrociclos de Cobalto (CoN4) e suas interações com o oxigênio por meio dos modelos de adsorção de Griffith (Side-on) e Pauling (End-on). As estruturas iniciais dos complexos Porfirina de Cobalto - CoP, Octametilporfirina de Cobalto - CoOMP, Tetrametilporfirina de Cobalto - CoTMP, Tetraaza[14]anuleno de Cobalto - CoTAA e Dibenzotetraaza[14]anuleno de Cobalto - CoDBTAA foram obtidas do programa GaussView e a otimização das geometrias e a distribuição de carga das estruturas, bem como as suas interações com o oxigênio molecular, foram realizadas com o uso do programa Gaussian 09. Os resultados obtidos comprovam que a estrutura dos ligantes do macrociclo influência a capacidade de ligação do O2 ao cobalto. Na avaliação da interação com oxigênio, a Porfirina de Cobalto e seus derivados mostraram uma melhor evidência, frente ao grupo Tetraaza[14]anuleno, para a interação com o oxigênio molecular devido ao enfraquecimento da ligação na molécula de O2, característica reforçada pelos dados provenientes da carga Mulliken. Portanto, a ordem de interação apresentada pelos complexos estudados é CoTMP, CoOMP, CoP, CoDBTAA e CoTTA no modelo End-on e CoP, CoOMP, CoTMP, CoDBTAA e CoTAA no modelo side-on.

Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-06-07T18:43:28Z No. of bitstreams: 1 LuzyannePereira.pdf: 2863158 bytes, checksum: ff3a4e65449af34c7e12b19e0f749f60 (MD5) / Made available in DSpace on 2017-06-07T18:43:28Z (GMT). No. of bitstreams: 1 LuzyannePereira.pdf: 2863158 bytes, checksum: ff3a4e65449af34c7e12b19e0f749f60 (MD5) Previous issue date: 2011-08-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / In this dissertation we present, by computational simulations based in the density functional theory implemented in the SIESTA code, a study on the electronic and energetic properties of face centered cubic (fcc) and body centered cubic (bcc) crystal strutures interspersed with FeCl3 and CrO3 molecules composed by fullerene C60. For this study we used LDA and GGA approximations to represent the exchange-correlation term. Our results suggest that fcc-C60 and bcc-C60 structures interspersed with FeCl3 and CrO3 molecules are stable in terms of the LDA approximation, with the structure interspersed with CrO3 being more energetically favorable . The electronic properties of these systems were analysed by means of projected density of states (PDOS). We have observed that the electronic properties of fcc-C60/bcc-C60 were a ect when interspersed with FeCl3 and CrO3 molecules. The pure fcc-C60/bcc-C60 structures are semiconductor materials with band gap energy around 1,58 eV. When the fcc-C60 interacts with FeCl3 and CrO3 molecules the band gap energy changes to 0.68 eV (semiconductor character ) and almost zero (metalic character), respectively. In the other hand, the bcc-C60 structure interacting with FeCl3 and CrO3 molecules presents metalic and semiconductor (with decreasing of the band gap from 1.58 to 1.20 eV) character, respectively. / No presente trabalho estudamos as propriedades energeticas e eletronicas do solido C60, nas estruturas cubica de face centrada e cubica de corpo centrado, intercalado com as moleculas FeCl3 e CrO3, atraves de simulacão computacional de primeiros princípios baseada na teoria do funcional da densidade, implementada no programa computacional SIESTA. Este estudo foi realizado considerando as aproximações LDA e GGA para o termo de troca e correlação. Analisando o resultado da interação do C60 nas estruturas fcc e bcc com as moleculas FeCl3 e CrO3, observamos que os sistemas sao mais estaveis na aproximacao LDA, sendo que o sistema CrO3/fcc (bcc) é energeticamente mais favoravel. As propriedades eletronicas destes sistemas sao analisadas atraves da densidade de estados projetada (PDOS). As propriedades eletronicas do solido C60 nas estruturas fcc e bcc puro sao afetadas pela intercalaçao das moleculas FeCl3 e CrO3. O C60 na estrutura fcc é semicondutor com gap de energia em torno de 1;58 eV, mas quando intercalado com a molecula FeCl3 veri camos que o sistema permanece semicondutor, com gap de 0;68 eV. Já para o sistema CrO3/fcc observamos que este passa a ser metalico. O C60 bcc puro é semicondutor, mas quando intercalado com a molecula FeCl3, o sistema passa a apresentar carater metalico. Enquanto que intercalado com o CrO3, o sistema permanece semicondutor com gap de energia reduzido para 1;20 eV.

This thesis studies the physics of multilayer heterostructures grown from topological insulators (TIs), primarily bismuth selenide and antimony telluride, and other topologically trivial materials. This is done by extending a standard low-energy 3D TI Hamiltonian and varying its associated material parameters across the simulation domain. New results arising from the position-dependent TI interface model are found. For the first time, this method is incorporated into a density-functional theory (DFT) solver in order to study the self-consistent charge density in multilayer TI heterostructures due to the interface states. The thesis is structured as follows. The introduction (Ch. 1) presents a pedagogical review of the theory of 3D TIs and low-energy Hamiltonians used to study them, as well as typical methods in solid state physics that are made use of throughout the thesis. Chapter 2 presents the position-dependent Hamiltonian, showing new evidence for topological features of bulk states including varying degrees of band mixing and inversion; also, interface state tunnelling is shown to be affected by atomic layer orbital overlap, and incomplete localisation of surface states is demonstrated for antimony telluride. Chapter 3 presents a new DFT model of TI heterostructure interfaces and shows how conduction through TI interface states can be controlled with an electric field. Chapter 4 covers the extension of the model in Ch. 1 to 2D cross-sections of TI wires and heterostructures, showing for the first time evidence of localisation of conduction almost entirely within the inner interfaces of a 2D heterostructure wire. Chapter 5 presents our work with magnetic fields, demonstrating evolution of interface and bulk states with changing magnetic field and Landau level, as well as presenting new evidence for more complex spin structures in bismuth selenide arising from Landé factor signs. Our conclusions are presented in Chapter 6.

This thesis is concerned with study of vibrational dynamics and their effect on charge transport in thin films of organic semiconductors. Two classes of organic semiconductors are investigated- crystalline small molecules and conjugated polymers. Although device performance of both classes of materials has greatly improved over last two decades, detailed understanding of relationship between structure and transport properties is still missing- so far development of organic semiconductors has mostly been based on experimental approach, with theoretical models providing post factum justification rather than guiding rational design of novel compounds. In this thesis I establish methodology to investigate both inter- and intramolecular vibrational modes by combining latest computational techniques with experimental pressure-dependent Raman spectroscopy. The dominant factor limiting charge delocalization in crystalline small molecules are low frequency, large amplitude intermolecular modes. However, theoretical modeling of these modes require use of periodic boundary conditions increasing computational cost by orders of magnitude when compared to commonly used vacuum phase simulations. I report comparative study of two implementations (CRYSTAL09 and CASTEP) of density functional theory (DFT) and dispersion correction (Grimme and Tkatchenko-Scheffler) and evaluate their applicability to predict low frequency vibrational modes in 2,7-Dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) and 2,8-Difl uoro-5,11-bis(triethylsilylethynyl)anthradithiophene (dif-TES-ADT). Charge transport in conjugated polymers is strongly affected by energetic disorder arising from spatial variations in backbone conformation. I combine vacuum phase DFT simulations of intramolecular vibrational modes with pressure-dependent Raman spectroscopy to study planarity and torsional backbone disorder of 2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene (pBTTT), indacenodithiophene-co-benzo-thiadiazole (IDT-BT), diketopyrrolopyrrole-benzotriazole (DPP-BTZ) and naphtalene-bithiophene (NDI-T2) at pressures up to 3.9 GPa. It is shown that Raman spectra of pBTTT and NDI-T2 demonstrate dependence of mode intensities on hydrostatic pressure, whereas spectra of IDT-BT and DPP-BTZ exhibit lack of dependence. Simulations of theoretical spectra performed as a function of backbone torsion indicate that pBTTT undergoes deplanarization of already non-planar backbone and that NDI-T2 backbone is planarized, whereas backbones of IDT-BT and DPP-BTZ are resilient to changes of conformation. Finally, I perform large scale molecular dynamics simulations of crystalline, semi-crystalline and disordered phases of IDT-BT and DPP-BT in order to investigate effect of disorder on backbone conformation. Both compounds were previously reported to exhibit extremely low degree of energetic disorder- I assign this phenomenon to their surprisingly strong resilience to side chain disorder. In both systems simulations demonstrate novel mechanism of disorder accommodation- their backbones bend rather than twist and retain low degree of torsional variation even in amorphous phase.

The emerging 2D materials are potential solutions to the scaling of electronic devices to smaller sizes with lower energy cost and faster computing speed. Unlike traditional semiconductors e.g. Si, Ge, 2D materials do not have surface dangling bonds and the short-channel effect. A wide variety of band structure is available for different functions. The aim of the thesis is to calculate the electronic structures of several important 2D materials and study their application in particular devices, using density functional theory (DFT) which provides robust results. The Schottky barrier height (SBH) is calculated for hexagonal nitrides. The SBH has a linear relationship with metal work function but the slope does not always equal because Fermi level pinning (FLP) arises. The chemical trend of FLP is investigated. Then we show that the pinning factor of Si can be tuned by inserting an oxide interlayer, which is important in the application to dopant-free Si solar cells. Apart from contact resistance, we want to improve the conductivity of the electrode. This can be done by using a physisorbed contact layer like FeCl3, AuCl3, and SbF5 etc. to dope the graphene without making the graphene pucker so these dopants do not degrade the graphene's carrier mobility. Then we consider the defect formation of 2D HfS2 and SnS2 which are candidates in the n-type part of a tunnel FET. We found that these two materials have high mobility but there are also intrinsic defects including the S vacancy, S interstitial, and Hf/Sn interstitial. Finally, we study how to make defect states chemically inactive, namely passivation. The S vacancy is the most important defect in mechanically exfoliated 2D MoS2. We found that in the most successful superacid bis(trifluoromethane) sulfonamide (TFSI) treatment, H is the passivation agent. A symmetric adsorption geometry of 3H in the -1 charge state can remove all gap states and return the Fermi level to the midgap.

Direct hydrocarbon fuel cells are fuel cells than use hydrocarbons directly as fuel instead of the most commonly used fuel in a fuel cell, hydrogen. Studies are being done on direct hydrocarbon fuel cells because they have the potential to be energetically more efficient than hydrogen fuel cells. There are many different hydrocarbons that are available to use as a feed stock and each one reacts at different reaction rates. As the current density of a fuel cell is linked to the reaction rate, it is important to know the energetics of an oxidation reaction that is occurring. Density Functional Theory (DFT) is a technique that can be used to predict the energy states of intermediate reaction steps in a given mechanism. The focus of this study is the using DFT to explore the energetics of the oxidation of ethane to ethylene in a nickel-anode catalyst fuel cell. DFT was used in adsorption runs to optimize the geometries beginning (adsorbed ethane) and end (adsorbed ethylene) of the oxidation reaction. DFT was then used to calculate the energy of transition states by varying bond lengths. It was determined the removal of the second hydrogen from the ethyl radical is the most energy intensive step and, thus, the rate limiting step. Hydrogen, ethane, and ethylene were all explored in this study. The heats of adsorption varied from largest to smallest in the order of ethylene, hydrogen, and ethane. It was determined that the heat of adsorption of hydrogen is sufficient to meet the energy requirements for the dissociation reaction. This may help explain why hydrogen reacts so readily in fuel cells. Conversely, the heats of adsorption for the hydrocarbons did not meet the energy requirements for the dissociation reactions. This may help explain why ethane and ethylene react more slowly in a fuel cell as compared to hydrogen. Also, the oxidation of ethane to ethylene requires two large activation energies. These two additional activation energies may help explain why ethylene reacts more readily than ethane in a fuel cell.

Submitted by Julio Henrique Hartmann (juliohenrique@msn.com) on 2018-04-16T06:15:34Z No. of bitstreams: 1 Dissertação_final Julio Henrique Hartmann.pdf: 2243165 bytes, checksum: dd94af85066e93f95365876d2a3c7e82 (MD5) / Approved for entry into archive by Raphael Vilas Boas (raphaelboas@ibict.br) on 2018-04-25T18:45:57Z (GMT) No. of bitstreams: 1 Dissertação_final Julio Henrique Hartmann.pdf: 2243165 bytes, checksum: dd94af85066e93f95365876d2a3c7e82 (MD5) / Made available in DSpace on 2018-04-25T18:45:57Z (GMT). No. of bitstreams: 1 Dissertação_final Julio Henrique Hartmann.pdf: 2243165 bytes, checksum: dd94af85066e93f95365876d2a3c7e82 (MD5) Previous issue date: 2014 / In this work we examined theoretically via computer simulation of first principles, the interaction of graphene with the molecules of resveratrol and quercetin. To do this, use the Density Functional Theory and the pseudopotential method as implemented in the SIESTA computer code. Resveratrol is an antioxidant drug and several studies have highlighted and proven the benefits of resveratrol health. This has been shown flavonoid chemopreventive, antioxidant, antiplatelet, antifungal, anti-inflammatory, cardioprotective, among others. Quercetin is the main flavonoid present in the human diet and its therapeutic properties have been studied in recent decades, highlighting the potential antioxidant, anticarcinogenic and its protective effects on renal, cardiovascular and hepatic systems, and also has antimicrobial activity. However, these two drugs are very unstable. In this regard, the main motivation is to use graphene with these two drug molecules to overcome the instability of the same, because of the properties of graphene Its primary is exactly be electrochemically stable. Our results show that the most stable configuration for the binding energy of quercetin with graphene was 0.93 eV and resveratrol value found for the binding energy was 0.53 eV indicating the occurrence of weak interaction through physical adsorption. Analyzing the band structure of the interacting systems, we found that no significant changes occur in the electronic properties compared to pure graphene. The stability of the molecules was improved due to charge transfer and the decrease of the total energy of the molecules. / Neste trabalho analisamos, teoricamente, via simulação computacional de primeiros princípios, a interação do grafeno com as moléculas de resveratrol e quercetina. Para isso, utilizamos a Teoria do Funcional da Densidade e o método de pseudopotenciais conforme implementados no código computacional SIESTA. O resveratrol é um fármaco antioxidante e vários estudos têm destacado e comprovado os benefícios do resveratrol à saúde. Este flavonóide tem demonstrado propriedades quimiopreventivas, antioxidantes, antiplaquetárias, antifúngicas, anti-inflamatórias, cardioprotetoras, entre outras. A quercetina é o principal flavonóide presente na dieta humana e suas propriedades terapêuticas têm sido estudadas nas últimas décadas, destacando-se o potencial antioxidante, anticarcinogênico e seus efeitos protetores aos sistemas renal, cardiovascular e hepático, sendo que possui também atividade antimicrobiana. Entretanto, estes dois fármacos são bastante instáveis. Neste sentido, a principal motivação do trabalho é utilizar o grafeno com estas duas moléculas de fármacos para suprir a instabilidade das mesmas, pois uma das propriedades precípuas do grafeno é justamente ser eletroquimicamente estável. Nossos resultados mostram que para as configurações mais estáveis, a energia de ligação da quercetina com o grafeno foi de 0,93 eV e para o resveratrol o valor encontrado para a energia de ligação foi de 0,53 eV indicando a ocorrência de interação fraca por meio de adsorção física. Analisando a estrutura de bandas dos sistemas interagentes, observamos que não ocorrem alterações significativas nas propriedades eletrônicas quando comparadas com o grafeno puro. Em relação à estabilidade das moléculas houve uma melhora devido à transferência de carga, à diminuição da energia total das moléculas e ao fato de que não houve alteração significativa na geometria dos sistemas.

Neste trabalho é introduzido e avaliado um conjunto de novas ideias para aumentar a eficiência do método Basin-Hopping Monte Carlo (BHMC) aplicado à otimização global de clusters e nanopartículas, que resultou no método BHMC revisado. Dentro deste método, tomou-se o cuidado de manter as características fundamentais do método BHMC padrão, que consistem na transformação da superfície de energia potencial em um conjunto de basins de atração, e no emprego de amostragem de Monte Carlo utilizando o critério de Metropolis. As ideias por trás do método BHMC revisado incluem um grande conjunto de operadores locais e não locais construídos especificamente para clusters e nanopartículas e que permitem maior mobilidade sobre a superfície de energia potencial durante a busca pelo mínimo global, duas estratégias de seleção de operadores, e um operador de filtro estrutural para remover soluções não físicas. A eficiência do método apresentado foi avaliada através da sua aplicação a um grande número de clusters e nanopartículas de tamanhos variados, compreendendo sistemas descritos tanto por potenciais empíricos, quanto por primeiros princípios dentro do formalismo da teoria do funcional da densidade (DFT). Os sistemas investigados foram clusters de Lennard-Jones e Sutton-Chen contendo até 148 átomos, um conjunto de nanopartículas de Lennard-Jones com tamanhos variando entre 200 e 1500 átomos, clusters binários de Lennard-Jones com até 100 átomos, clusters binários de metais de transição (AgPd)55 descritos pelo potencial de Sutton-Chen, clusters de alumínio puros com até 30 átomos descritos por DFT, e clusters de alumínio com até 15 átomos dopados com um átomo de cobre, também descritos por DFT. Através da otimização global sem bias de todas essas partículas, o método BHMC revisado foi capaz de reproduzir com sucesso os mínimos globais putativos mais recentes disponíveis na literatura obtidos por diversas técnicas de otimização global, e também foi capaz de identificar mínimos globais previamente desconhecidos. Além disso, em comparação com o método BHMC padrão, o método RBHMC mostrou maior eficiência para muitos dos sistemas investigados. As ideias contidas na metodologia apresentada constituem uma ferramenta valiosa para auxiliar investigações teóricas visando uma melhor compreensão da estrutura atômica de clusters e nanopartículas. / In this work it is introduced and evaluated a set of new ideas to increase the efficiency of the Basin-Hopping Monte Carlo (BHMC) method applied to the global optimization of clusters and nanoparticles, which resulted in the revised BHMC method. Within this method, care was taken to keep the main features of the standard BHMC method, which are the transformation of the potential energy surface into a set of basins of attraction, and the use of Monte Carlo sampling employing the Metropolis criterion. The ideas behind the revised BHMC method include a large set of local and non-local operators built specifically for clusters and nanoparticles which allow a greater mobility over the potential energy surface along of the search for the global minimum, two strategies for selecting the operators, and a structural filter operator to remove unphysical solutions. The efficiency of the presented method was evaluated by applying it to a large number of clusters and nanoparticles of various sizes, comprising systems described both by empirical potentials and by first-principles within the formalism of density functional theory (DFT). The systems that were investigated were Lennard-Jones and Sutton-Chen clusters with up to 148 atoms, a set of Lennard-Jones nanoparticles with sizes from 200 to 1500 atoms, binary Lennard-Jones clusters with up to 100 atoms, binary transition metal clusters (AgPd)55 described by the Sutton-Chen potential, pure aluminum clusters with up to 30 atoms described by DFT, and aluminum clusters with up to 15 atoms doped with a copper atom, also described by DFT. Through the unbiased global optimization of all those particles, the revised BHMC method was able to successfully reproduce the most recent putative global minima available in the literature obtained by several different global optimization techniques, and moreover, it was able to identify previously unkown global minima. Furthermore, in comparison with the standard BHMC method, the RBHMC method proved to be more efficient for many of the systems that were investigated. The ideas comprised within the presented methodology characterize a valuable tool for aiding theoretical investigations leading to a better understanding of the atomic structure of clusters and nanoparticles.

Desde a identificação do vírus da imunodeficiência humana (HIV, do inglês Human Immunodeficiency Virus) como agente causador da Síndrome da Imunodeficiência Adquirida (AIDS ? do inglês Acquired Immunodeficiency Syndrome), a busca para tratamentos seguros e eficazes contra o HIV transformou-se no principal foco para a descoberta de uma nova droga em todo o mundo. A AIDS aparece como um dos principais problemas de saúde pública para as próximas décadas, onde será o maior determinante de mortalidade na faixa etária entre 20 e 50 anos em praticamente todos os países do mundo. Tendo como objetivo relacionar a atividade de compostos biflavonóides anti-HIV-1 com algumas de suas propriedades moleculares, serão utilizados métodos de Mecânica Molecular e Química Quântica. O método de cálculo semi-empírico AM1 foi empregado para calcular um conjunto de propriedades moleculares dos 14 compostos biflavonóides com atividade anti-HIV-1. A seguir utilizar-se-á métodos estatísticos com a finalidade de separar os 14 compostos em duas classes, ativos e não ativos, de forma que se relacione qual as propriedades, dentre as calculadas, são responsáveis pela atividade dos compostos biflavonóides estudados. As técnicas estatísticas utilizadas foram a Análise de Componentes Principais (PCA: Principal Components Analysis), Análise Hierárquica de Agrupamentos (HCA: Hierarquical Clusters Analysis) e Análise de Discriminates por Passos (SDA: Stepwise Discriminant Analysis). Os estudos com PCA, HCA, e SDA mostraram que as variáveis HOMO (Highest Occupied Molecular Orbital - Orbital Molecular Ocupado de Maior Energia), LUMO (Lowest Unoccupied Molecular Orbital ? Orbital Molecular Desocupado de Menor Energia), e Área superficial são responsáveis pela separação dos compostos com alta e baixa atividade anti-HIV-1. O comportamento destas três propriedades pode ser útil na tentativa de se obter outros compostos biflavonóides com elevada atividade inibidora anti-HIV-1. / A set of 25 quinone compounds with anti-trypanocidal activity was studied by using the Density Functional Theory (DFT) method in order to calculate electronic atomic and molecular properties to be correlated with the biological activity. The chemometric methods Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA), Stepwise Discriminant Analysis (SDA), Kth nearest neighbor (KNN) and Soft Independent Modeling of Class Analogy (SIMCA) were used to obtain possible relationships between the calculated descriptors and the biological activity studied and predict the anti-trypanocidal activity of new quinone compounds from a test set. Four descriptors were responsible for the separation between the active and inactive compounds: T5 (torsion angle), HOMO-1 (energy of the first molecular orbital below HOMO), QTS1 (sum of absolute values of the atomic charges) and VOLS2 (volume of the substituent at region B). These descriptors give information on the kind of interaction that occurs between the compounds and the biological receptor. The prediction study was done with a set of three new quinone compounds by using the PCA, HCA, SDA, KNN and SIMCA. Beside the five chemometric methods, the neural network method was used by employing the backpropagation algorithm. The four variables (T5, QTS1, VOLS2 and HOMO-1) were employed to validate the models constructed previously. The architecture of networks consisting of four neurons at input layers, ten neurons at intermediary layers and two neurons at output layers was adopted to observe the root mean square error between the true and desired output over the entire training set. The percentage of correct classification was 87.5%, and only one compound was predicted wrong in the test set, which indicates that the model is robust and could be able to make predictions. The docking studies were carried out with two different programs in the approach of ligands: the Autodock and FlexX. The docking results on trypanothione reductase enzyme showed that all studied compounds stay at second hydrophobic pocket in the outer region of the active site called the Z-site. The residues that could be specifically involved in the binding of ligands are Lys62, Thr66, Thr397, Thr463, Leu399, Ser464, Glu466 and Glu467, where the residues Thr66, Thr463 and Leu399 are conserved in different trypanothiones and could be used for the development of selective inhibitors against to the parasite enzyme.

Simulações computacionais são ferramentas essenciais para a compreensão num nível microscópico de diversos fenômenos que ocorrem na natureza. Em particular, simulações ab initio, isto é, de primeiros princípios, podem predizer novas propriedades e auxiliar na interpretação de resultados experimentais, sem a necessidade de potenciais empíricos os quais são ajustados para uma específica configuração do sistema. No entanto, mesmo para simulações ab initio são necessárias aproximações tanto para o cálculo de estrutura eletrônica quanto para a descrição dos movimentos nucleares. Nesta tese, novas aproximações para o funcional de energia de troca e correlação da Teoria do Funcional da Densidade (DFT) são propostas e testadas no cálculo de estrutura eletrônica de átomos, moléculas e sólidos. Para a descrição dos movimentos nucleares a técnica de Monte Carlo é utilizada, porém as energias totais são obtidas com a DFT. Propomos também uma nova metodologia que permite descrever movimentos intramoleculares de sistemas cujas frequências de vibração não podem ser tratadas classicamente. Como aplicações estudamos aglomerados de água e água líquida, mostrando a relevância dessa nova metodologia na descrição de propriedades estruturais, vibracionais e de momento de dipolo desses sistemas. / Computer simulations are essential tools for a microscopic understanding of many processes that occur in nature. In particular, ab initio simulations, i.e., first principles simulations, can predict new properties and support experimental results, without the need to use empirical potentials which are fitted for a specific configuration of the system. However, even in ab initio simulations it is necessary to do approximations for the electronic structure calculations and for the description of the nuclear movements. In this thesis, new approximations for the exchange-correlation energy functional of Density Functional Theory (DFT) are proposed and tested for atoms, molecules and solids. The description of the nuclear movements was done using the Monte Carlo technique, however the total energy calculations were obtained by DFT. We also propose a new methodology which allows the description of intramolecular movements whose vibrational frequencies can not be treated classically. As an illustration, we have studied water clusters and liquid water, showing the relevance of this new methodology on the description of structural, vibrational and of the dipole moment of these systems.