Phase coexistence in clusters: An “experimental” isobar and an elementary model

This work examines the temperature dependence of the coexistence ratios of phaselike forms of atomic clusters of two kinds, a homogeneous cluster bound by pairwise Lennard–Jones forces that simulates Ar55, and a binary, ionic cluster simulating (KCl)32. Two methods have been used: isothermal molecular dynamics and a simple analytical model based on highly simplified densities of states. The phase behavior of the alkali halide cluster is well represented by a two-level density of states, a nondegenerate lower level, and a highly degenerate upper level. The phase behavior of the argon cluster needs an intermediate level of moderate degeneracy to reproduce the three-phase behavior of the simulations.