Equilibrium State of a Metal Slab and Surface Stress

First-principles full-potential all-electron total-energy calculation on a 7-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 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 on the surface region determined by fitting the energy differences permit evaluation of the surface stress as 5.28 mRy/bohr²=4.11 joule/m². The surface region material is found to be less stiff than bulk.