This was modelled by CO adsorption on two separated Pt1 monomers, as illustrated in Figure . Note that this configuration with two next-nearest neighbor Pt surface atoms along the <210> direction represents the one with the closest Pt -Pt possible for non-neighbored surface atoms. Starting with adsorption of a single CO on one of the two Pt surface atoms in Figure (left), we find that electronic Pt-Pt interactions do not affect the CO adsorption energy on one of these Pt surface atoms. With 2.06 eV it is identical to that obtained for adsorption on a Pt1 monomer in a Pt1Ag8/Pt(111) unit cell (Figure