Similarly to the approach described in our previous work, we have doped the top layer of a ε-TaN(1 1 0) slab with W and Co. To do this, 25%, 50% or 100% of the Ta atoms in the top layer were replaced with the dopant. The surfaces will be labelled as W dopant-concentration or Co dopant-concentration , giving for example W 25 for 25% W doping or Co 100 for 100% Co doping. There are two coordination environments for metal atoms in the TaN (1 1 0) surface. The S-site forms a six coordinate structure with N, while the F-site is three coordinate with N. In our previous work, we found that Ru doping is more favourable at the F-site than the S-site, and that the number of dopants at each site affects the stability of the surface. This is also the case for Co and W doping. For 50% doping, we chose two different doping distributions , namely the most and least favourable 50% dopant distributions.