Adsorption of CO on TiO2(110) studied by means of a cluster model surrounded by multipoles obtained from slab calculations

An array of point multipoles is used to mimic the long-range Coulomb interactions in a TiO56- cluster model designed to describe the adsorption of CO on a rutile surface. The multipoles are derived from the electron density and the concomitant electrostatic potential of a slab model of the (110) surface of rutile as calculated in a periodic Hartree-Fock approach. The motivation for the use of a cluster model is the possibility of inclusion of electron correlation by means of quantum-chemical methods, which is to date not easily possible in periodic Hartree-Fock calculations. In contrast to an array of point charges based on a Mulliken population analysis of the periodic charge distribution, the distributed multipoles show good agreement of adsorption properties as compared to a slab calculation. Surface relaxation has a significant influence on the binding of the adsorbate.