A SYSTEMATIC INTERMOLECULAR POTENTIAL METHOD APPLIED TO CHLORINE

A systematic method is described for finding effective model intermolecular pair potentials to use in realistic simulations of condensed phases. The pair potential is split up into electrostatic, dispersion and repulsion components, all of which may be parametrized by using ab initio monomer wavefunctions. The repulsion energy is estimated by a novel method that assumes proportionality to the overlap between the unperturbed charge densities. The resulting model includes atom-atom anisotropy in all three components of the potential in a realistic, theoretically justified manner. One parameter has to be obtained from elsewhere, in this case by fitting to solid state data. More parameters can be adjusted in order to absorb errors such as the neglect of many-body effects. Application of this method to chlorine gives a model with four fitted parameters that predicts many properties of the solid and liquid at least as accurately as the best modern potential, which has eight fitted parameters.