Phase Changes in Icosahedral 54-, 55-, 56-Atom Platinum Clusters

Abstract

Using the Voter and Chen version of an embedded-atom model, derived by fitting simultaneously to experimental data both the diatomic molecule and bulk platinum, we have studied the melting behavior of free, icosahedral, 54-, 55- and 56-atom platinum clusters in the molecular dynamics simulation technique. We present an atom-resolved analysis method that includes physical quantities such as the root-mean-square bond-length fluctuation and coordination number for individual atoms as functions of temperature. The effect of a central atom in the icosahedral structure to the melting process is discussed. The results show that the global minimum structures of the 54-, 55- and 56-atom Pt clusters do not melt at a specific temperature, rather, melting processes take place over a finite temperature range. The heat capacity peaks are not delta-functions, but instead remain finite. An ensemble of clusters in the melting region is a mixture of solid-like and liquid-like clusters.