Cargas atomicas (um novo modelo) : implementação computacional e aplicações

AUTOR(ES)

Alexandre Araujo de Souza

DATA DE PUBLICAÇÃO

1994

RESUMO

In the present work a computational implementation and a subsequent application of a new atomic charge model are made. This new model was derived after 1990, when a new partition of the atomic polar tensor (APT) was done, in terms of charge, charge flux, atomic dipole flux and homopolar dipole flux. An APT of an atom in a molecule, represented by a 3x3 matrix, is the gradient of the molecular electric dipole moment, with respect to the infinitesimal changes in cartesian atomic coordinates. The new atomic charge model was defined as an invariant (1/3 of the trace) of the total charge tensor (TC). The TC is a sum of the charge (Mulliken) diagonal tensor with the atomic part of the homopolar dipole flux. In this way, the new model can be seen as a correction for the well known Mulliken net charges. The definition of the new model, in terms of a total charge tensor is expected to be better than a model based on the TPA, as occurs in Cisolowski model, defined as 1/3 of the trace of the TPA. The computational implementation was dane with the development of two programs, in FORTRAN language, that read the output of the GAMESS public domain ab initio software package and calculates the total charge tensor, in the Hartee-Fock leveI. Then, calculations are made for some molecules and the quality of the new model is compared with respect to Mulliken, Cioslowski and electrostatic potential models. It is seen that the new model describes correctly several situations, including some in which Mulliken and Cioslowski are wrong. The nitrous acid (HONO), s-cis and s-trans, are specially studied, as applications of the new model. The atomic charges obtained by the use of the new model, show some stability with respect to changing the basis set and they can reproduce (with a few exceptions) the ab initio molecular dipole moment and electrostatic potential better than Mulliken and Cioslowski charges. The new model also describes well the internal redistribution of charges as HONO goes from s-cis to s-trans form. The new model can correct the Mulliken charges in the rigth direction.

ASSUNTO(S)

computadores carga atomica processamento eletronico de dados fisico-quimica

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