Influence of the intermolecular electrostatic potential on properties of polar polarizable aprotic solvents

Abstract

The liquid properties of models of acetonitrile, acetone and chloroform are calculated within the framework of the hypernetted chain approximation of the molecular Ornstein—Zernike theory. The shape of a molecule is described by a set of Lennard-Jones sites. Its electrostatic properties are modelled either by the first multipole moments up to the octopole or by partial charges, and by a point polarizability tensor. The multipole moments and the partial charges are computed by ab initio molecular orbital methods. In the liquid phase, the polarizability is taken into account by calculating an effective induced point dipole moment using a self-consistent mean-field approximation. While the Lennard-Jones part of the internal excess energy is nearly independent of the description of the electrostatic interaction and of the polarizability, the electrostatic part and the dielectric constant change notably. The models with the partial charges lead to dielectric constants which are in good agreement with the experimental data, provided that the molecular polarizability is correctly taken into account. The internal excess energies are also correctly predicted except for acetone. How the approximation of the intermolecular electrostatic interaction modifies the liquid structure is studied by investigating the dominant bimolecular configurations. These configurations allow one to understand better why the Kirkwood factor changes with the electrostatic description. The Ornstein—Zernike formalism is a practical tool for studying with light numerical effort how the liquid properties depend on the intermolecular interaction. It can help in the development of new accurate potentials for liquid simulation.