Equilibrium state of a metal slab and surface stress

First-principles full-potential all-electron total-energy calculations on a seven-layer Mo(001) slab have found the equilibrium state of the slab and the energies of nearby states produced by isotropic two-dimensional (epitaxial) strain. In the slab equilibrium state, the in-plane lattice constant contracts 1.7% and the out-of-plane lattice constant contracts 0.7% from bulk values. The energy differences of these nearby states strained from equilibrium have been fitted to a composite elastic model of the slab which has two surface regions and a bulk region, each with three elastic parameters. The parameters of the surface regions determined by fitting the energy differences permit evaluation of the surface stress as (Formula presented) The surface region material is found to be less stiff than the bulk. © 1999 The American Physical Society.