From molecular clusters to bulk matter. I. Structure and thermodynamics of small CO2, N-2, and SF6 clusters

摘要

The thermodynamics and structural properties of small molecular X-N clusters (X=N-2, CO2, and SF6) are investigated using molecular dynamics simulations. In this paper we compare the behavior of carbon dioxide, nitrogen, and sulfur hexafluoride for a given cluster size of N=13. Evidence is provided for "dynamical coexistence" between solidlike and liquidlike forms of the cluster, in a finite energy range, in the case of (CO2)(13) and (N-2)(13) but not (SF6)(13). In addition (N-2)(13) exibits a solid-solid phase transition characterized by the release of the molecular orientational degree of freedom. A systematic use of the dynamic quenching method enables us to interpret these different behaviors in terms of the energy distribution of minima in the potential energy surface of the systems. A comparison of the strain energies of these clusters, using a model recently proposed by Wales and co-workers, enables us to understand why different molecular clusters exhibit different crossover points from icosahedral to bulk properties. (C) 1998 American Institute of Physics. [S0021-9606(98)00425-5]. [References: 46]