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

New combining rules are proposed for the well depth, epsilon, and inte raction distance, sigma, describing nonbonded interatomic forces for r are gas pair interactions. Concepts underlying current combining rules ''applied in simulations of macromolecular and polymer systems are sh own to be incompatible with experimental data on the rare gases. The c urrent combining rules are compared with the new results using the exp erimental data. Mathematical properties of combining rules are conside red, 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 graph ically analyze combining rules against experimental data. We demonstra te using this analysis technique that the rare gas potentials do not o bey 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 pre dict the epsilon parameters for the mixed rare gas pairs. (C) 1993 by John Wiley & Sons, Inc.