We use a simple electronic model for the cohesive energy of metals which explicitly considers eigenfunctions and eigenvectors in a single-particle linear-combination-of-atomic-orbitals approach. From them forces are obtained to perform molecular-dynamics calculations or static relaxation. As an application we compare the model predictions to full many-body ab initio and embedded-atom-model calculations applied to structure and energetics of small Na and Al clusters, to bulk Al, and to vacancies in Al. The relevance of the angular forces introduced by the symmetry of the orbitals used is clearly reflected. Advantages and limitations of this approach as well as size restrictions are discussed.

• Received 24 July 1989

DOI:https://doi.org/10.1103/PhysRevB.41.913