Aplicações de formulação hidrodinâmica da mecânica quântica a sistemas moleculares

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Curso de Pós-Graduação em Físico-Químic

Estimating the Octanol/Water Partition Coefficient for Aliphatic Organic Compounds Using Semi-Empirical Electrotopological Index

A new possibility for estimating the octanol/water coefficient (log P) was investigated using only one descriptor, the semi-empirical electrotopological index (ISET). The predictability of four octanol/water partition coefficient (log P) calculation models was compared using a set of 131 aliphatic organic compounds from five different classes. Log P values were calculated employing atomic-contribution methods, as in the Ghose/Crippen approach and its later refinement, AlogP; using fragmental methods through the ClogP method; and employing an approach considering the whole molecule using topological indices with the MlogP method. The efficiency and the applicability of the ISET in terms of calculating log P were demonstrated through good statistical quality (r > 0.99; s < 0.18), high internal stability and good predictive ability for an external group of compounds in the same order as the widely used models based on the fragmental method, ClogP, and the atomic contribution method, AlogP, which are among the most used methods of predicting log P

Estrutura eletrônica e propriedades magnéticas de Pd3FE

Orientador: Edson Zacarias da SilvaTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb WataghinResumo: Neste trabalho estudamos as propriedades eletrônicas e magnéticas da liga Pd3Fe. Estudamos a fase ordenada do Pd3Fe empregando o método Iinear de orbitais muffin-tin com a aproximação das esferas atômicas, o qual é de primeiros princípios e inclui polarização de spin. Os resultados teóricos de propriedades térmicas e magnéticas mostram boa concordância com a experiência. Explicamos aqui a formação de momentos magnéticos localizados a partir de elétrons completamente delocalizados. Investigamos a influência do hidrogênio nas propriedades físicas do composto Pd3Fe, onde obtivemos uma redução drástica nos momentos magnéticos nos sítios de Pd e Fe, o que é corroborado pela experiência. Usamos os potenciais convergidos do composto Pd3Fe ferromagnético para analisarmos a influência da desordem na estrutura eletrônica do Pd3Fe. Empregamos para isso uma versão que inclui polarização de spin, do método da função de Green com a aproximação do potencial coerente (ou KKR-CPA). Os resultados assim obtidos mostram que em ligas aleatórias ferromagnéticas ocorrem diferentes graus de desordem para as diferentes direções de spin. Explicamos a formação dos momentos magnéticos nestas ligas a partir da existência de estados de 'cristal virtual' para elétrons com spin up e de estados de 'bandas separadas' para elétrons com spin down. Por último empregamos os orbitais muffin-tin para calcularmos o espectro de fotoemissão de raios-X dos compostos Pd3Fe e Pd3FeH, o que nos permite uma estreita conexão com a experiênciaAbstract: In this work we study the electronic and magnetic properties of the Pd3Fe alloy. For the ordered phase of Pd3Fe we employed the Linear Muffin-Tin Orbitals Method, with the atomic sphere approximation, which is a first principles method and includes spin polarization. The theoretical results for the thermal and magnetic properties show good agreement with experience. Here we explain the formation of the localized magnetic moments from completely itinerant electrons. We investigate the influence of the hydrogen in the physical properties of the compound Pd3Fe, where we obtain a drastic reduction in the magnetic moments at the Pd and Fe sites. This reduction is confirmed by experience. The self consistent potentials of the Pd3Fe compound were used for an analysis of the influence of the disorder in the electronic structure of Pd3Fe alloy. To this end, we employ a spin polarized version of the Green¿s Function Method with the Coherent Potential Approximation (or KKR-CPA).The results obtained show that in random ferromagnetic alloys different degrees of disorder occurs for the different spin directions. The formation of the magnetic moments in these alloys were explained from the existence of 'virtual crystal' states for spin up electrons and 'split band' states for spin down electrons. Finally we employ the muffin-tin orbitals to calculate the X-ray photoemission spectra of the Pd3Fe and Pd3FeH compounds, which allows us a direct comparison between theory and experimentDoutoradoFísicaDoutor em Ciência

Estudo das ligações de hidrogênio para dímeros formados pelas moléculas de H2O, NH3, HF, HCl e HBr através de cálculos baseados em primeiros princípios

Hydrogen bond energies of fifteen dimers were calculated using the large basis set 6-311++G(3df,3pd), at Hartree-Fock (HF) level including Møller-Plesset (MP2) calculations. The procedure for obtaining such energies were based on the dimer's energy rise provoked by increasing in intermolecular distance of the system component units. Deviations from a strictly linear hydrogen bond were investigated and rotational barriers were also computed allowing the calculation of the second order attractive interactions. In order to provide a more objective definition of hydrogen bond, a lower energy limit was proposed in place of the merely empirical parameters employed in the classical definitio