SLAB VERSUS CLUSTER APPROACH FOR CHEMISORPTION STUDIES - CO ON CU(100)

Local density functional (LDF) slab calculations exhibit good converge nce for the chemisorption energy with the number of substrate layers a nd with the adsorbate-adsorbate distance, in contrast with the poor co nvergence with cluster size and shape commonly observed in cluster cal culations. The major discrepancy of cluster calculations for Cu/CO wit h experiment, i.e. strong preference for the hollow site, does not rec ur in the slab calculations, although the hollow site is still slightl y preferred. The local density approximation yields an overbinding of almost-equal=to 75 kJ/mol, at top sites in line with the LDA overbindi ng for metal-ligand bonds and for bond energies in general.