Influence of multiatom interactions on the shapes and energetics of two-dimensional homoepitaxial clusters on close-packed metallic surfaces.

Abstract

We describe a scheme (BSM for ``bond saturation model'') for modeling the energetics of adatom clusters on close-packed metallic surfaces. In the BSM, atoms interact via coordination dependent nearest-neighbor bonds. We show that the BSM yields a detailed understanding of the relationship between shape and energy for two-dimensional (2D) homoepitaxial adatom clusters on close-packed metallic surfaces. In particular, we advance a simple rule for predicting the binding energies of small clusters based on the moments of their coordination distributions, derive a useful expression for the binding energy of a 2D cluster of arbitrary geometry, and study the role played by coordination dependent bonding in determining step energies for adatom islands. Our analysis of step energies provides insight into why the two distinct types of monatomic steps on Pt(111) have similar free energies as observed by Michely and Comsa. While our numerical results are for Pt(111), we expect our conclusions to hold for any chemically similar system. \textcopyright{} 1996 The American Physical Society.