WEAK INTERACTION POTENTIALS OF LARGE CLUSTERS DEVELOPED FROM SMALL CLUSTER INFORMATION

The task of finding readily calculable potentials for intermediate-sized and very large clusters and molecular assemblies is important in view of their need in surface, droplet, and condensed-phase simulations. However, the most detailed probes of weak interaction, which are gas-phase or matrix isolation experiments, involve small, isolated species and mostly binary complexes. The connection between the information from those experiments and the potentials for many interacting molecules can come about only with a clear, physical understanding of the major elements of weak interaction. Standard ideas about electrical interaction have often been useful for understanding small clusters, especially where the electrical analysis is done at a high level. This seems, therefore, to be a most useful physical basis for developing potentials. A particular aspect the role of electrical polarization, has been found to be important in certain ways in a number of binary clusters even though it is usually a small energetic contributor. More significant is that polarization may be the crucial link with clusters of more than two submolecules since it is necessarily a nonpairwise or cooperative interaction. Within this framework, the strategies for extrapolation of small cluster pictures to realistic potentials for large clusters are considered. © 1990 American Chemical Society.