Kinetics of nonequilibrium shape change in gold clusters

The properties of gold clusters AuN with N from 40 to 800 have been studied using constant temperature molecular-dynamics simulations and an empirical potential. A solid-liquid transition is clearly identified for this size range. For clusters of size N>150 it is also seen that surface atoms of a cluster start to diffuse well below the melting point. We also study the kinetics of shape change from an initial nonequilibrium elongated state to a final, close to equilibrium, compact shape. It is found that the radius of gyration rg that reflects the cluster shape decays by different mechanisms depending on the temperature and cluster size. At most temperatures large solid clusters coalesce smoothly by surface diffusion, while smaller solid clusters maintain their nonequilibrium shape for a long time and then coalesce abruptly.