The differences in CO adsorption energies on the interface (ii) site on the one hand and on the interface (i) site and the middle layer site on the other hand are again mainly due to larger (positive) contributions from the COad induced deformation energies and changes in the interface energies, which are reflected by the larger difference between CO binding energy and CO adsorption energy (Figure ). These change little upon variation of the O-vacancy position, except in the presence of the O-vacancy on the (ii) site. In this case, both the CO binding energy as well as the sum of deformation and interface energies contribute to the higher CO adsorption energies (Figure ).