  Molecular dynamics simulations show that gold clusters with about 600--3000
atoms crystallize into a Mackay icosahedron upon cooling from the liquid. A
detailed surface analysis shows that the facets on the surface of the Mackay
icosahedral gold clusters soften but do not premelt below the bulk melting
temperature. This softening is found to be due to the increasing mobility of
vertex and edge atoms with temperature, which leads to inter-layer and
intra-layer diffusion, and a shrinkage of the average facet size, so that the
average shape of the cluster is nearly spherical at melting.
