Cálculo de propriedades elétricas lineares, não-lineares e estruturais da molécula HOBr
AUTOR(ES)
Ricardo Spagnuolo Martins
FONTE
IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia
DATA DE PUBLICAÇÃO
09/04/2010
RESUMO
Ab initio, also known as first principles, computational methods are highly esteemed because of the accuracy of the results produced and the fact that they are not built upon any empirical models, therefore considered reliable. Although, these positive remarks carry along a heavy computational effort, which increase very rapidly with the number of basis functions used in the calculation. This work calculates equilibrium structures, vibrational frequencies, dipole polarizability and first hyperpolarizability of the molecule HOBr. This molecule is inserted in the ozone depletion process as a more eficient catalyst in the destruction of ozone molecules than CFCs. The objective is to come up with a basis function that is small, so it may reduce the computational effort, but at the same time suficiently polarized and diffuse so that it may retain the accuracy of larger and more complete functions that are available from the literature. Also, due to the size of the bromine atom, the use of and effective core potential was made. The functions used in this work were assembled using substrate and polarization functions available from the literature. The diffuse functions were obtained using the even-tempered method. Calculations were performed in the HF, CCSD and CCSD(T) level of theory. The results were consistent with experimental values and other ab initio calculations of this molecule. Also, there was a significant reduction of the computational time in comparison to functions with similar number of basis functions. Equilibrium structures rely on low-range valence electron interaction. Therefore, less diffuse functions were necessary and the use of ECP for bromine was justified. Harmonic frequencies rely both on polarization and diffuse functions for the valence electrons, although not to a great extent. Therefore, an average polarization with addition of diffuse functions and ECP produced good results with small computational effort. (Hyper)polarizabilities were very strong dependent on long range interaction of all the electrons, so this property was better represented by an average polarization and highly diffuse basis set.
ASSUNTO(S)
física da matéria condensada teoria molecular funções harmônicas teorias não-lineares condensed matter molecular theory harmonic functions nonlinear theories
