(1a) and not that of the natural Ag bulk, as in reference . Using the natural bulk Ag as a reference would increase the calculated surface energy by half of the compression energy of the 12-layer bulk (see below), i.e., by about 18 meV Å -2 (Table ). The similar magnitude of the surface energies can at least qualitatively be explained by the fact that for the laterally compressed Ag the distances between Ag layers are larger and therefore the surface bonds are weaker than for bulk Ag. On the other hand, due to the larger unit cell of bulk Ag there are fewer Ag -Ag bonds per surface area, which seems to compensate the weaker bonding per Ag surface atom. For the pseudomorphic Ag film covered surfaces, we find a significantly higher surface energy for the monolayer film (Ag1L), while for the bilayer (Ag2L), and trilayer (Ag3L) Ag films the surface energies closely resemble that of the pure Ag surfaces. Based on the principle of constant bond order, one would expect the opposite effect for the Ag1L system. Since the Pt -Ag bonds are stronger than Ag -Ag bonds, one would expect the bonds of the Ag surface layer to another Ag layer, which are broken during crystal cleavage, to be weaker than similar bonds in a pure Ag system. Such discrepancies had been explained by long-range effects, which must be present on top of short range effects following the bond-order principle. For the surface alloys, we considered two cases, one where the underlying Pt atom is underneath a PtAg2 hollow site and one where this is underneath a Ag3 hollow site. In both cases, the surface energies are considerably higher than obtained for the Ag bulk and Ag multilayer films, but lower than that of the Ag1L system.