The compression energies of the different Ag/Pt(111) systems, which are indicated as grey bars in Fig. , were calculated via the Ag compression energy per Ag atom, 𝐸 𝐴𝑔 𝑃𝑡 0 , using the 12-layer Ag unit cell once with the natural lattice and once with the vertically relaxed Pt(111) lattice (see eq. ( )). As expected, the compression energies are positive and increase steadily from the Ag1L to the Ag3L system. For the mixed layer in the Pt@Ag1L systems, where the Ag compression and thus the compression energy is not well defined, we estimated the compression energy as ¾ of the compression energy in the Ag1L system, based on the Pt0.25Ag0.75 composition. Therefore, this should be considered as a qualitative estimate.