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

Local density functional (LDF) slab calculations exhibit good convergence for the chemisorption energy with the number of substrate layers and with the adsorbate-adsorbate distance, in contrast with the poor convergence with cluster size and shape commonly observed in cluster calculations. The major discrepancy of cluster calculations for Cu/CO with experiment, i.e. strong preference for the hollow site, does not recur in the slab calculations, although the hollow site is still slightly preferred. The local density approximation yields an overbinding of almost-equal=to 75 kJ/mol, at top sites in line with the LDA overbinding for metal-ligand bonds and for bond energies in general.