A Semi-Empirical Potential for Simulations of Transition Metal Clusters: Minima and Isomers of Nin (n=2-13) and their Hydrides

A potential energy surface (PES) for bare, mono and di-hydrogenated nickel clusters is constructed using the extended-Huckel approximation. The parameters are optimized and good agreement with theoretical and experimental results is obtained without including a posteriori coordination dependent terms. The global minimum and the first few low-lying isomers of several nickel clusters are investigated using a variety of minimization techniques. The difference in energy between isomers is much smaller than the Ni-Ni dissociation energy. Both geometric and optical isomers are found for many cluster sizes. In some cases symmetric nuclear configurations give rise to orbital degeneracies in the adiabatic surface which lead to distortions. The hydrogen atom is most frequently found on the surface. All isomers of NinH2 contain a dissociated hydrogen molecule. The results are in good agreement with quantitative and qualitative experimental findings on this system.