Melting of 55-atom Morse clusters

Abstract

Canonical ensemble Monte Carlo simulations of 55-atom Morse clusters are used to study the effect of the range of the pair interaction on the cluster melting transition. Several different structural indicators are employed to monitor the solid–liquid transition and to locate the melting and freezing temperatures. The behavior of Landau free energy curves in the solid–liquid phase coexistence regime is correlated with the distribution of inherent minima sampled by the system. The melting transition temperatures, the width of the phase coexistence regime, and the internal energy change on melting are shown to increase with decreasing range of the pair interaction, which parallels the behavior seen in bulk Morse systems. Unlike in the case of bulk melting, cluster melting falls into three distinct categories based on the range of the pair interaction: (i) a rigidity transition in long-range systems with a low density of metastable states, (ii) the cluster analogue of bulk melting where the system transits from the basin of an ordered global minima into a set of metastable, amorphous packing minima, and (iii) transition from a set of defected solid-like minima into a set of amorphous packing minima.