Multi-dimensional entropy sampling Monte Carlo method and free energy landscape of Ar13

A multi-dimensional entropy sampling Monte Carlo method is proposed and implemented to evaluate directly the entropy of a 13-atom argon cluster (Ar13). The Helmholtz free energy of the cluster is obtained and expressed as a function of the clusterʹs energy E and radius of gyration Rgy at several temperatures. A transition zone where the accessible range of Rgy varies rapidly is found to be the coexistence region of the solid-like and liquid-like structures.