Symmetry and site selectivity in molecular chemisorption: Benzene on Ni{111}

We discuss the results of large-scale density functional calculations for (7×7) benzene adsorption on the ferromagnetic substrate Ni{111}. Adsorption at the bridge site, with C–C bonds parallel to the [2̄11] direction, is found to be energetically preferred over the [1̄10]-oriented hcp site suggested by electron diffraction experiments. We discuss the roles of intermolecular forces and anisotropic molecular vibrations in accounting for this apparent discrepancy. Furthermore, our analysis of charge and spin densities clarifies the relationship between preferred adsorption sites and the symmetry of frontier molecular orbitals.