Cluster calculation of carbon monoxide on a Cu surface using the self-consistent-field-Xα-scattered-wave method

Two geometries of CO chemisorbed on a Cu(100) surface have been studied using the self-consistent-field-$X\alpha$-scattered-wave method. Both geometries assume the CO molecule is bonded to the Cu surface with the C end down; one geometry is in the fourfold symmetric hole site and one is directly on top of a Cu atom. The calculated valence density of states for the fourfold-symmetry case gives a satisfactory interpretation of the two main peaks below the copper $d$ band in the uv photoemission spectra (UPS). A third weaker peak of the UPS data can be correlated with a CO molecule adsorbed directly on top of a copper atom.