Cu 3d covalency in chemisorption?

Two problems are addressed in the present study: the degree of copper 3d covalency involved in the chemisorption of oxygen at the fourfold hollow site of Cu(100) and the separability of the correlation energy into contributions from the 3d shells on copper and from the valence sp band. The investigation was carried out at the all-electron level using a Cu5 cluster as a model of the Cu(100) surface. The analysis shows that the 3d covalency is of practically no importance in the system considered, contributing only 1–3 kcal/mol to the total chemisorption energy of 89 kcal/mol. The correlation energy was found to be separable to within 5 kcal/mol. A configuration-interaction calculation on the Cu5O system using the one-electron effective core potential developed previously yielded a correlation energy in close agreement with the all-electron results.