Combination rules for intermolecular potential parameters. II. Rules based on approximations for the long-range dispersion energy and an atomic distortion model for the repulsive interactions.

Combination rules for intermolecular potential parameters based on the identification of the attractive term of the potential function with different expressions for the long-range dispersion energy and the introduction of an improved model for the combination of repulsive potentials are derived and applied to the Lennard-Jones (12–6) and Kihara potentials. The ability of the rules to predict interaction virial coefficients and unlike-pair potential parameters obtained from viscosity data is examined. Results are compared to those obtained in similar tests in part I of this study. Combination rules based on the London dispersion formula and an assumption of a geometric mean rule for the distances at which the repulsive forces are in equilibrium are shown to have advantages over previously proposed rules for the two potential functions assumed.