CO adsorption on SnO2(110): cluster and periodic ab initio calculations

The adsorption properties of CO molecules on the SnO2(110) surface have been investigated by means of quantum-mechanical calculations. The oxide surface has been represented by clusters of ions embedded in point charges or by periodic slabs of various thickness. The methods used to compute adsorption energies, geometries and vibrational modes are Hartree–Fock and density functional theory. Coverage and surface relaxation effects have been explicitly considered. The bonding and vibrations of adsorbed CO have been analyzed by decomposing the interaction energy into the sum of various contributions. This analysis shows that the interaction of CO with the five-coordinated Sn ions of the surface has a large electrostatic character reinforced by a substantial donation of charge from CO to the cation. The CO adsorption is rather weak; the adsorption energy is ∼0.25 eV, but is accompanied by a large shift of the vibrational frequency towards higher values (Δω≈+80 cm−1).