Structure and Transformation. Clusters as Models for Condensed Phases

Abstract

The special advantages and characteristic limitations of molecular clusters in investigations of the properties of condensed phases are evaluated. Clusters naturally lend themselves to the exploration of (1) the possible ways molecules can pack while undergoing various degrees of thermal agitation, and (2) the cooperative behavior of molecules in transitions between phases. Clusters can be studied experimentally, in expanding supersonic jets, or computationally, in molecular dynamics simulations. Of particular interest are clusters of polyatomic molecules because their structural diversity is much richer than that of atomic clusters. Novel phases not seen in the bulk have been generated, and explained. Extraordinarily rapid nucleation rates have been observed at the extremely high supercoolings that can be attained. Interfacial free energies of boundaries between liquid and solid phases have been inferred. Clusters are versatile and effective model systems of great promise in research on condensed matter.