The influence of O-vacancies in O-vacancy clusters in deeper layers underneath the Ru nanorod on the CO adsorption energy is illustrated in Figure (see also Table ). Starting with an O-vacancy on the (1i) site (1VO), the vacancy cluster grows by formation of additional O-vacancies at the neighboring ii, iii, and iv sites in deeper layers, with the resulting systems being denoted as 2VO, 3VO, and 4VO. Also in this series we have to consider a few changes in adsorption site / behavior. During optimization, CO adsorbed on the edge site of the top layer relaxes to a hollow site formed by the 7a, 8a, and 5a Ru atoms in the 2VO and 4VO systems (Table ). CO adsorbing on the interface (i) site in the 2VO system dissociates into C and O. Therefore, the related CO adsorption energy is not included in Figure . For the 3VO and 4VO systems, CO adsorbing at the interface (i) site (1a, 5a) relaxes to a threefold hollow site formed by the Ru-2a, Ru-4a and Ru-5 atoms (Table ) (hatched bars in Figure ). Furthermore, CO adsorbed at the interface (ii) site relaxes to a bridge site composed of 4a and 6a for the 2VO -4VO systems (Table ) (hatched bar in Figure ).