Due to the more pronounced total charge transfer to the Ru nanorod, the presence of an O-vacancy cluster directly underneath the Ru nanorod may lead to stronger effects in CO adsorption than the single O-vacancies discussed so far. Following the procedure in section 3.1.1, we started by removing the surface oxygen atom from site 1i, followed by removal from the 2i and 3i sites, forming the 1VO, 2VO, and 3VO clusters.