STRUCTURE AND ENERGETICS OF MODEL METAL-CLUSTERS

A Finnis-Sinclair-type many-body potential and a combined Lennard-Jones (two-body) plus Axilrod-Teller (three-body) potential are employed to study the structural properties of model clusters in the size range 13 to 309 atoms. For the first potential, parameter values for the fcc transition metals as proposed by Sutton and Chen are used, while for the latter potential a least-squares fitting routine is employed to fit the parameters to bulk data. For suitable parameter ranges, the relative energies of optimized decahedral, icosahedral, and face-centered-cubic (fcc) cuboctahedral clusters are compared in the light of experimental observations for these metals. Variation of the parameters in the Finnis-Sinclair potential, which govern the range of the repulsive two-body term and the attractive many-body term, influences the size at which the icosahedra and fcc cuboctahedra cross over in energy. Similarly, an increase in the three-body contribution in the LJ + AT clusters leads to a decrease in the crossover size from several thousand to a few hundred atoms. For appropriate parameter ranges, a convex curvature of the facets as well as a contraction of the clusters is observed for both potentials. These effects are compared with experimental observations for the fcc transition metals copper, silver, gold, nickel, palladium, and platinum.