A detailed theoretical study of the electronic structure of an ordered $c(2\mathrm{}\times 2)$ oxygen overlayer adsorbed on a Ni(001) surface is performed using the layer-Korringa-Kohn-Rostoker multiple-scattering method. Effects on the local density of states due to the extended nature of the substrate as well as adsorbate-adsorbate interactions are discussed. Emphasis is placed upon the different role of Ni $4s$ and $3d$ states in forming bonds with the oxygen $2p$ levels. The interaction with the $3d$ bands leads to a splitting of the $p$ levels into bonding states below and unfilled antibonding states above the $d$ bands. These states extend approximately two layers deep into the substrate although in specific regions of the surface Brillouin zone related to the bulk band structure, they may become considerably longer ranged. Interference with the Ni $s-p$ band broadens the oxygen-induced states up to 0.5 eV, the width depending on orbital symmetry and on ${\overrightarrow{\mathrm{k}}}_{\parallel }$. Both bonding and antibonding states are split apart due to the anisotropy of the crystal potential at the surface. Their absolute as well as relative energies are shown to vary with ${\overrightarrow{\mathrm{k}}}_{\parallel }$. The results are in qualitative agreement with several spectroscopic observations.

• Received 29 July 1977

DOI:https://doi.org/10.1103/PhysRevB.17.1653