SIMULATION OF ADSORBATE-INDUCED SURFACE RECONSTRUCTION

Adsorbed atomic monolayers of atoms such as carbon and nitrogen can cause substantial reconstructions of a nickel {001} surface. In this simulation we combine an atomic-orbital-based calculation of electronic structure with an empirical pair-wise repulsive potential to model the covalent part of the total energy. For 0.5 monolayer coverage by the adsorbate, the surface metal layer relaxes into a p(2 x 2) structure, with transverse displacements of about 0.4 angstrom. At the same time these displaced surface nickel atoms ride up above second layer nickels, with a vertical displcement of about 0.4 angstrom. The covalent contribution to the relaxation energy comes out at about 2.0eV per carbon atom and 1.4eV per nitrogen atom, of which the reconstruction contributes about 0.3 eV.