NEW COMBINING RULES FOR RARE-GAS VAN-DER-WAALS PARAMETERS

New combining rules are proposed for the well depth, epsilon, and interaction distance, sigma, describing nonbonded interatomic forces for rare gas pair interactions. Concepts underlying current combining rules ''applied in simulations of macromolecular and polymer systems are shown to be incompatible with experimental data on the rare gases. The current combining rules are compared with the new results using the experimental data. Mathematical properties of combining rules are considered, and it is shown how to reduce combining rule formulas from a two-parameter to a single-parameter problem. It is also shown how to graphically analyze combining rules against experimental data. We demonstrate using this analysis technique that the rare gas potentials do not obey a single combining rule for the epsilon parameter but do follow a single combining rule for the sigma parameter. Finally, we demonstrate that a combining rule using both epsilon and sigma can be used to predict the epsilon parameters for the mixed rare gas pairs. (C) 1993 by John Wiley & Sons, Inc.