Discussion of the electronic properties of these surfaces based on Bader charges and density of states (DOS) plots are included in the Supporting Information, Section S7. The DOS is metallic for all structures studied. Given the comparatively smaller number of Cu, Co and W atoms compared to the TaN slab, the DOS is dominated by metallic TaN. We find that the contributions of Co to the total DOS are stronger than those of W and Cu. The Bader charges show, that Cu atoms tend to be more oxidised on the Co-doped surfaces compared to Ru-and W-doped TaN. On all thermally stable surfaces, as for systems we previously studied, Cu atoms are only oxidised if they interact directly with the surface, while all other Cu atoms remain metallic. These electronic properties should yield reasonable Cu resistivity, which is essential for Cu interconnects.