Local-orbital analysis of the oxygen–nickel (001) bond from self-consistent electronic structure

We have calculated self-consistently the electronic structure of a model of a c(2×2) oxygen overlayer on the nickel (001) surface using the linearized augmented-plane-wave method, obtaining good agreement with the experimentally measured electronic excitation spectra. Our purpose has been to analyze the charge density, wave functions, bond orders, local densities of states, and energy levels to obtain a picture of the bonding between the oxygen and the nickel surface. We find that the oxygen 2p states hybridize more strongly with the nickel 4s4p bands than with the 3d bands, and we demonstrate that the optimal local orbitals for the oxygen nucleus which span the resulting 2p-like bands centered at $E_F$-5.5 eV resemble large oxygen 2p orbitals. Bond orders exhibit the bonding nature of these states and the existence of antibonding states above $E_F$.