Similar to the results for a single O-vacancy at different positions underneath the Ru nanorod (Figure ), the effect on the adsorption energy of CO on the top layer and the middle layer site is negligible. Adsorption at the middle layer site is again slightly more stable than on the top layer site, which we explained before by the lower coordination of the Ru-5a atom in the middle layer. An essentially constant adsorption energy is obtained also for adsorption on the interface (i) site, with the exception that there is no stable adsorption on this site for the 0VO and 2VO systems, where COad either moves to the middle layer site (0VO system) or dissociates ) and does not lead to CO dissociation any more. Hence, similar as for the individual O-vacancies in deeper layers (Figure ), the additional O-vacancies do not affect the charge on this adsorption site in an O-vacancy cluster. A similar trend is observed also for the charge transfer between CO, Ru nanorod and support (Figure ), with a rather constant transfer of about -0.35 e to CO adsorbed on the interface (i), both from the Ru and from the support. This seems to be dominated by the presence of the O-vacancy at the 1i site, with little effect from additional, deeper lying O-vacancies. Finally, Figure indicates that the CO adsorption energy largely follows the CO binding energy. Hence, the pronounced changes in the deformation and interface energies observed for the 1VO system essentially cancel out.