Melting in small gold clusters: a density functional molecular dynamics study

Molecular dynamics simulations of the thermal behaviour of gold clusters containing 7, 13 and 20 atoms have been performed. Total energies and forces at each step of the simulation are calculated from first principles using density functional theory. Ion trajectories are then calculated classically from these forces. In each case the global minimum energy structure and a low-lying isomer are used as the starting structures. In most cases, the clusters do not exhibit a sharp transition from a solid-like phase to a liquid-like phase, but rather pass through a region of transformations between structural isomers that extends over a considerable temperature range. Solid-like behaviour is observed in the atomic trajectories of the simulation at temperatures up to, or above, the bulk melting point. The 20-atom tetrahedral structure is the one exception, showing a sharp transition between solid-like and liquid-like phases at about 1200 K. The starting structure used in the simulation is shown to have a considerable effect upon the subsequent thermal behaviour.