For single atom adsorption, increasing the number of Cu-surface bonds increases the overall stability of the adsorption. At site X, which is the least favourable site, the Cu adatom is bound to a single chalcogen atom. B, where the adatom binds to two chalcogenide atoms, is the second least stable site on each monolayer. M and H allow the Cu adatom to bond to three chalcogen atoms, and are therefore the two most stable adsorption sites for single atoms. M is likely the most stable of all four sites as the presence of an atom here is a continuation of the WX 2 crystal structure. Interestingly, as the size of the chalcogen species increases, the difference in stability between M and H decreases, with the difference being 0.12, 0.08, and 0.04 eV on the sulphide, selenide, and telluride respectively.