Thermodynamics of small platinum clusters

Abstract

Using the Voter and Chen version of an embedded atom model, derived by fitting simultaneously to experimental data of both the diatomic molecule and bulk platinum, we have studied the melting behavior of free, small platinum clusters in the size range of N=15–19 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 results show that as the Pt15–Pt18 clusters exhibit multistage melting, melting in Pt19 cluster takes place in a single but interesting stage. None of these melting stages occurs at a specific temperature, rather, melting processes take place over a finite temperature range. This range is larger for less symmetric clusters. An ensemble of clusters in the melting region is a mixture of different isomeric forms of the clusters. The multistage melting and the occurrence of a single melting stage over a temperature range are two different phenomena.