Ab initio model potential and molecular dynamics simulation of Ag-6 clusters

We present an approach to generate a model potential with parameters fitted to ab initio energetic surfaces. The potential includes two-, three- and four-body terms. Each of them consists of an exponential exchange and dispersion terms. The analytical form of the latter was taken from perturbation theory up to fourth order. We illustrate the present approach by constructing an ab initio model potential for the Ag-6 cluster. A molecular dynamics simulation using this potential reveals interesting features in the isomerization of the C-2v structure. A two step isomerization transition is observed: First, at temperatures around 350 K, the cluster structures fluctuate between two-dimensional isomers. At higher temperatures (450 K), fast transitions occur between two- and three-dimensional cluster configurations.