A LCAO-LDF STUDY OF FORMATE CHEMISORPTION ON CU(100)

The coordination of formate on the Cu(100) surface has been investigated by using the LCAO-LDF molecular-cluster approach. Two different adsorption geometries, the short bridge and the cross bridge, have been investigated. In the former coordination, the adsorbate/substrate bonding is mainly sigma in character, while in the latter pi interactions, even though rather weak, seem to play a leading role. In both cases the molecular orbitals responsible Of the Cu-0 bonding have been identified. Total energy calculations indicate that the short bridge configuration is more stable than the cross bridge one by about 20 kcal/mol. Furthermore, a good agreement with experimental (ARPEFS, SEXAFS, XPD) structural parameters and formate ARUPS data is obtained only for the short bridge local geometry.