LCAO-LDA STUDY OF THE CHEMISORPTION OF FORMATE ON CU(110) AND AG(110)SURFACES

The coordination of formate on the Cu(110) and Ag(110) surfaces has be en investigated by coupling density functional theory to the molecular -cluster approach. Two adsorption sites, the bidentate bridging (BE) a nd the bidentate chelating (BC), have been considered for both surface s. In the BE arrangement, the HCOO oxygen atoms bridge two adjacent me tal (M) atoms in the (110) direction, while in the BC form they chelat e a single M atom. Adsorption energies, optimized geometries and vibra tional frequencies of the surface HCOO at the BE and BC sites have bee n computed. Furthermore, the molecular orbitals involved in the adsorb ate-substrate interaction have been identified. Independently of the c hemisorption site geometry, the HCOO-Cu(110) bond is computed to be st ronger and more covalent than that of HCOO-Ag(110). Total energy calcu lations indicate that the BE coordination site of the Cu(110) surface is favoured, with respect to that of BC by ca. 1.0 eV. Despite the nea rest neighbour Ag-Ag internuclear distance being longer than that of C u-Cu, theoretical results pertaining to HCOO on Ag(110) again indicate that the BE site is more stable than that of BC by ca. 0.7 eV.