Physics of nickel clusters: Energetics and equilibrium geometries

The equilibrium geometries and the binding energies of Ni-n clusters (n less than or equal to 23) have been calculated by using an empirical many-body potential and molecular dynamics (MD) simulation, For small clusters, the potential is found to reproduce the geometries based on first-principles density functional calculations. It is shown that the clusters do not mimic the bulk structure and undergo significant geometrical changes with size. The binding energy per atom, on the other hand, increases monotonically with size. The evolution of the geometries is found to be correlated with the underlying changes in the nature of bonding. An analysis of the fragmentation channels based on the ground state energies shows the loss of the Ni dimer to be the most energetically favorable channel. The calculated geometries are compared with those derived from recent experiments on N-2 adsorption on Ni-n clusters.