In total, the effect of the O-vacancies on the CO adsorption strength is rather small in these cases, less than 0.2 eV at most, which is significantly less than the difference in adsorption energy between adsorption on top layer or interface (ii) sites on the one hand and middle layer or interface (i) sites on the other hand. Furthermore, the CO adsorption energy does not vary much with the position of the vacancy underneath the Ru nanorod. The general difference between adsorption on the different interface sites seems to mainly result from the differences in the (positive) contributions from the sum of the COad induced deformation energies and changes in the interface energies between these sites, which are more pronounced for adsorption on the interface (ii) site than for adsorption on the interface (i) site, leading to lower adsorption energies on the interface (ii) sites. The remaining small changes in the CO adsorption energy for different positions of the O-vacancies seem to largely follow the trend given by the charge on the respective Ru adsorption sites and by the position of the d-band center. For adsorption on the top layer and middle layer sites, the small O-vacancy induced changes in the charge state or the CO adsorption energy reflect an effective metallic screening of the transferred charge.