A noticeable exception to this however is Se-Triangle-M (see figure ). This structure has a dramatically reduced metal-surface interaction energy, and forms the least stable of all Triangle structures. The metalsubstrate energy, is ∼ 0.2 eV less for Se-Triangle-M compared to the other stable structure on the selenide monolayer, whereas typical variations in metal-surface energies due to changing adsorption site are less than 0.10 eV. In Se-Triangle-M, all three Cu atoms migrate to coordinate above a single selenide atom, while remaining in a 2D triangle structure, which is not seen on either the WS 2 or WTe 2 monolayer. On WS 2 the sulphur atom is likely not large enough to allow for coordination with three Cu atoms at once, while the Te species is too large to allow this coordination -1.42 eV Although generally the adsorption sites do not notably affect the stability of the adsorbed cluster, not all adsorption sites are equally stable. For example, site H is typically an unstable site for multiatom adsorption; of the 24 configurations initially adsorbed on this site, only 1 multiatom structures fully relaxes to be adsorbed at this site, Te-3DRectangle-H.