and Table (Co-doped TaN). All Co-doped surfaces rearrange to some degree upon Cu adsorption, creating gaps on the surface that trap the Cu atom, depending on the adsorption site. This is due to the difference in ionic radius between Co (0.55 or 0.61 Å, depending on spin) and Ta (0.72 Å). While for TaN and all W-and Ru-doped surfaces the 5 coordinate site A is most favourable, only Co 50-S shares this most favourable adsorption site. On