Surface thermal stability of nickel clusters

Overall and surface melting of Ni-N clusters have been studied using Monte Carlo simulation and effective interaction model potential. Physical quantities such as internal energy per atom, specific heat, and bond length fluctuations are calculated as a function of temperature to illustrate overall and surface thermal softening of these clusters. It is found that the surface melting temperature is lower than the overall melting temperature for a Ni cluster of certain size. The results show that tile surface and core atoms play different roles in the melting process. The recent experimental observations about metal cluster melting might be explained by using surface melting arising from the surface atom disorder first appearing due to an increase of temperature.