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 been investigated by coupling density functional theory to the molecular-cluster approach. Two adsorption sites, the bidentate bridging (BB) and the bidentate chelating (BC), have been considered for both surfaces. In the BB arrangement, the HCOO oxygen atoms bridge two adjacent metal (M) atoms in the (1[1 with combining macron]0) direction, while in the BC form they chelate a single M atom. Adsorption energies, optimized geometries and vibrational frequencies of the surface HCOO at the BB and BC sites have been computed. Furthermore, the molecular orbitals involved in the adsorbate–substrate interaction have been identified. Independently of the chemisorption site geometry, the HCOO–Cu(110) bond is computed to be stronger and more covalent than that of HCOO–Ag(110). Total energy calculations indicate that the BB coordination site of the Cu(110) surface is favoured with respect to that of BC by ca. 1.0 eV. Despite the nearest neighbour Ag–Ag internuclear distance being longer than that of Cu–Cu, theoretical results pertaining to HCOO on Ag(110) again indicate that the BB site is more stable than that of BC by ca. 0.7 eV.