The Melting Process of Pd_(54) Cluster

Using Gupta potential,we performed molecular dynamics simulation to study the melting properties of Pd_(54) cluster with a center vacancy.Considering the core atoms play important role in the melting process and the core atoms with a vacancy is less stable than core atoms without vacancy,the cluster will exhibit two different melting processes.In this study,increase of the total energy leads to decrease of the temperature at the structural transition stage,which generally means that the negative heat capacity occurs.But,for Pd_(54) cluster,there is an irreversible transition from a structure with a center vacancy to that with a vertex vacancy.Because of this irreversibility of structural transition,the system prefers to keep the structure of the isomer and has a weak fluctuation during the most time of equilibrium, and the weak fluctuation of potential energy means that the fluctuation of kinetic energy is also weak and not cause to negative heat capacity.