Ab initio study of the intermolecular interactions in small benzene clusters: The equilibrium structures of trimer, tetramer, and pentamer

Correlated (MP2) calculations with 6-31G and 6-31G* basis sets have been us ed to probe the equilibrium geometries of the benzene trimer, tetramer, and pentamer. The lowest energy configuration was found to be a trigonal C-3h structure for the trimer and a tetrahedral C-3 structure for the tetramer. For the pentamer, the MP2/6-31G calculation yields the lowest energy struct ure, which is a trigonal bipyramid (C-3h) In the tetramer and pentamer, the fourth and fifth benzene molecules occupy the apex of the trigonal bipyram id with their molecular plane perpendicular to the 3-fold symmetry axis of the cyclic trimer motif. These structures, which maximize nearest-neighbor coordination number, suggest manifestation of the Wefelmeier growth sequenc e in benzene clusters.