Cluster studies of CO adsorption. III. CO on small Cu clusters

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Abstract
Chemisorption of CO on (100) and (111) Cu surfaces has been investigated by calculations on a series of small clusters. The dependency of the results on both the adsorption site (top or hollow) and the size of the cluster has been analyzed using a decomposition of the adsorption energy in various terms (steric repulsion, σ bonding, π backbonding). Some properties, i.e., M–CO distance, M–CO vibration, C–O distance, can be obtained from small cluster calculations as they are determined by ‘‘local’’ bonding aspects, whereas, e.g., the adsorption energy is not reliable due to delocalized features of the bonding being not well represented by small clusters. The deficiency of small clusters in modeling the polarizability of a metal substrate is stressed.