As described in section 3.1, the bulk formation energies contain contributions from the compression of the guest material in the pseudomorphic films, in this case Ag, and from additional interactions between Ag and Pt, on top of the average of the Ag -Ag and Pt -Pt interactions. In a simple picture, e.g., for the description of a deposit Ag film on a metallic Pt(111) substrate, this is also termed as interface energy.