While for the non-restructured systems it first continues to up-shift and then down-shifts again, the trend is opposite for the restructured systems. For comparison, the CO adsorption energy remains almost constant when going to the 3VO system and decreases when going to the 5VO system. Since also the interaction between CO and the 1Zr cation does not change (Table ), the question for the physical origin of the pronounced decay in CO adsorption energy in the 5VO system must remain open. Most likely, these changes are too small to be reproduced by the more qualitative nature of the d-band model. In this case, the trend in the CO adsorption energy mostly follows that in the CO binding energies, while changes in the deformation energies and in the interface energies seem to largely compensate each other.