MODELING CALCIUM AND STRONTIUM CLUSTERS WITH MANY-BODY POTENTIALS

Many-body atomistic potentials, of the Murrell-Mottram (MM) type, obta ined by fitting properties of solid phases of calcium and strontium [J .E. Hearn, R. L. Johnston, S. Leoni, and J. N. Murrell, J. Chem. Sec. Faraday Trans. 92, 425 (1996)], have been used to study the structures , stabilities, and growth modes of Ca and Sr clusters. Full structure optimization on small clusters (2-20 atoms) leads to structures involv ing the fusion of tetrahedral units, and predicts icosahedral cluster growth. Radial relaxation studies on icosahedral, truncated decahedral , cuboctahedral, and rhombic dodecahedral geometric shell clusters, le ad to the prediction that icosahedral structures are preferred until a round 32 000 (Ca) and 128 000 (Sr), whereupon the fcc-like cuboctahedr al clusters became preferred. These results are consistent with experi mental findings. A detailed analysis has been performed of the binding energies and radial expansion factors of each set of symmetry equival ent atoms (subshell). As for Lennard-Jones clusters, multishell icosah edral Ca and Sr clusters are predicted to undergo significant core com pression, resulting in low binding energies for the central atom and i nner shells. (C) 1997 American Institute of Physics.