A SEMIEMPIRICAL POTENTIAL FOR SIMULATIONS OF TRANSITION-METAL CLUSTERS - MINIMA AND ISOMERS OF NI-N (N = 2-13) AND THEIR HYDRIDES

A potential energy surface (PES) for bare, mono and di-hydrogenated ni ckel clusters is constructed using the extended-Huckel approximation. The parameters are optimized and good agreement with theoretical and e xperimental results is obtained without including a posteriori coordin ation 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 op tical isomers are found for many cluster sizes. In some cases symmetri c nuclear configurations give rise to orbital degeneracies in the adia batic surface which lead to distortions. The hydrogen atom is most fre quently found on the surface. All isomers of NinH2 contain a dissociat ed hydrogen molecule. The results are in good agreement with quantitat ive and qualitative experimental findings on this system. (C) 1998 Ame rican Institute of Physics.