Molecular adsorption on the surface of strongly correlated transition-metal oxides: A case study for CO/NiO(100)

It is well known that the physical properties of some transition-metal compounds (mostly oxides) are strongly affected by intra-]atomic correlations. Very recently, investigations of the adsorption of small molecules such as CO on the surfaces of transition-metal oxides have led to rather surprising results: the weak adsorbate-substrate bonding and the asymmetric (tilted) adsorption geometries contrast sharply the strong bonding and symmetric geometries characteristic for metallic surfaces. Calculations based on either Hartree-Fock or density-functional methods have failed to explain these observations. For bulk transition-metal oxides it has been demonstrated that the addition of a Hubbard-type on-site Coulomb repulsion U to the local-density Hamiltonian leads to an improved description of the electronic structure of these materials, but a consistent description of all physical properties proved to be elusive. In the present work, we present a comprehensive investigation of bulk NiO and of clean and CO-covered NiO(100) surfaces. We demonstrate that adding the on-site Coulomb repulsion to the spin-polarized gradient-corrected density-functional Hamiltonian leads to a consistently improved description of a wide range of cohesive, electronic, and magnetic properties of NiO (bulk and surface) and a very accurate description of the adsorption properties of CO. The effects of the strong electronic correlations in the substrate on the adsorbate-substrate bonding are discussed in detail.