For Neighbouring adsorption two stable adsorption modes dominate. On WS 2 , both S-Neighbour-X and S-neighbour-H relax to a structure where the Cu adatoms are adsorbed at neighbouring X sites. It is interesting that even though site H is more stable than X for single atom adsorption, neighbouring adsorption at H is an unstable structure, relaxing to form the same configuration as S-Neighbour-X. This is likely as bond formation between the two Cu atoms can be maximised with both atoms adsorbed atop neighbouring chalcogenide atoms. This shows that even for the smallest possible copper clusters, the competition between Cu-Cu bonds and Cu-surface bonds is dominated by intercopper bonding, rather than copper to surface bonds.