A Monte Carlo study of the structure and thermodynamic behaviour of small Lennard-Jones clusters

Abstract

Using a Monte Carlo method, the structure and phase behaviour of Lennard-Jones clusters composed of 13, 19 and 55 particles have been investigated. In contrast to most previous work, the clusters were placed in a hard constraining sphere of varying diameter, which allowed the canonical ensemble to be correctly simulated and all thermodynamic variables to be properly defined. In all the clusters the liquid-solid transition could be readily detected by observing the changes in radial density distribution functions and in thermodynamic quantities. For the 55 atom cluster, a two phase region was observed, characterized by a drastic increase in heat capacity of the system. In this case the cluster was composed of a solid core of 13 atoms, surrounded by a fluid-like shell. At high pressures and low temperatures the 19 and 55 atom clusters underwent a solid-solid transition.