The discrepancy between the trends for CO adsorption energy and C-O frequency is most likely due to the additional interaction of the CO with the 1Zr ion Changing to modifications in the CO vibrational properties upon formation of O-vacancies in a growing O-vacancy cluster underneath the Ru nanorod we find no significant differences to the effect induced by individual O-vacancies for CO adsorption on the top layer and middle layer sites, consistent with the generally weak effects of the O-vacancies on CO adsorbed on these sites (Figure , right panel).Note that in this case neighbored O-vacancies had to be considered to simulate a growing O-vacancy cluster (O-vacancies at position 1i, 2i 3i, 4i, 5i).