Structure and dynamics of small metallic clusters on an insulating metal-oxide surface: Copper on MgO(100)

We report density functional calculations of the structural and dynamical p roperties of small copper clusters (Cu-n, n = 2-5) adsorbed on MgO(100). As Cu-Cu intracluster interactions are stronger than cluster-surface interact ions, the most stable geometries are found to be similar to those in the ga s phase, with the cluster in an upright position with respect to the surfac e. Further ab initio molecular dynamics simulations indicate that the adsor bed clusters diffuse by "rolling" and "twisting" motions, with barriers tha t may be smaller than that for the hopping diffusion of a single adatom.