Density functional study of the adsorption of CO on Fe()

Density functional studies for the clean Fe(110) surface and for the adsorption of CO on Fe(110) at a half and a quarter monolayer CO coverage are reported. For the clean surface, we find only a modest surface relaxation and a modest increase of the magnetic moment of the first surface layer. At low CO coverage, CO adsorbs on top of Fe. But at half coverage, the density functional calculations predict that an off symmetry position between the hollow and bridge site results in the largest binding energy. Comparison of the vibrational frequencies with experiment however suggest, that the experimentally observed situation corresponds to atop adsorption at both coverage. Possible reasons for the discrepancy are discussed.