Molecular dynamics simulation of the melting-like transition in K1Na54

A set of molecular dynamics simulations at constant total energy has been performed in order to investigate the melting-like transition of the impurity-doped cluster K1Na54. An orbital-free density-functional-theory technique is employed to obtain the forces on atoms in an efficient way. The total simulation time is approximately 1.5 ns, which is required to obtain statistically meaningful thermal averages. The presence of just one K impurity reduces considerably the melting temperature value (as compared to Na55). Although only one peak is observed in the thermal evolution of the specific heat, analysis of the diffusion constants shows that the cluster melts in two separate steps: Na atoms are able to diffuse at lower temperatures than the K impurity.