ON THE COMPACT STRUCTURE OF SMALL FCC METAL-CLUSTERS

The general structure of small fcc metal clusters was investigated thr ough the use of site energies, i.e., interaction energy per atom as a function of coordination. We used only experimental data on the dimer binding energy, the surface energy, and the bulk cohesive energy to de termine these energies for all 15 fcc metals. These showed that real f cc metal systems exhibit a slight bond weakening as the number of bond s increases. It is also demonstrated that experimental data are much c loser to the limit of constant bond energy than to that of constant in teraction energy per atom. The constant bond energy model leads to com pact structures which maximize the number of bonds, and thus we predic ted that real small cluster systems would also be compact. Using molec ular dynamics/Monte Carlo corrected effective medium theory, which nea rly duplicates the experimental site energy curves, we studied the str uctures of 13-atom clusters of fcc metals via repeated melting and que nching in computer simulations. The lowest-energy structure was found to be a compact icosahedron with very high symmetry in every case. We also performed such simulations in the presence of a SiO2 support and found that the 13-atom Pt cluster maintained its nearly icosahedral sh ape. (C) 1994 Academic Press, Inc.