Energetics of small Pt clusters on Pt(111): Embedded-atom-method calculations and phenomenology

We have employed the embedded-atom method (EAM) to predict the structures and energetics of clusters containing up to seven Pt atoms adsorbed on the Pt(111) surface. The calculated cluster binding energies depend primarily on the number of (nearest-neighbor) bonds between the adatoms. Clusters with the same number of adatoms divide, according to their binding energies, into subgroups (bond families) of clusters with a common number of bonds. The typical spread of binding energies in these bond families is less than 0.2 eV, while the separation between neighboring families corresponds to a mean bond strength of about 0.7 eV. Thus the most stable clusters assume geometries which maximize the number of bonds. In addition, we propose a scheme for modeling the energetics of metal adatom clusters on close-packed metal surfaces whose physical basis is the coordination dependence of metallic bonds. With a simple three-parameter model, we predict binding energies of over 20 Pt clusters in excellent agreement with the EAM calculations. The scheme provides a convenient way of including many-atom interactions in the energetics of two-dimensional (2D) metallic clusters, and should, therefore, be useful for studying the equilibrium properties of 2D metallic surfaces