These results can be compared with those obtained in a recent in situ microscopy study of alloying and de-alloying of Ag and Pt in Ag films on Pt(111) and of a combined Monte Carlo and DFT study of segregation phenomena in Pt/Ag(111) systems. Exploring the growth and alloying /dealloying behavior of Ag on Pt(111) at about 800 K, Jankowski et al. observed a complex dynamic behavior with increasing Ag deposition, confirming alloy formation in the first monolayer and subsequent dealloying at Ag coverages of more than 70 % of a monolayer equivalent, by formation of monolayer islands with rather large Pt-rich central areas and Ag-rich rim areas. The observation of PtAg monolayer surface alloy formation even at these temperatures underlines that this is not mainly due to kinetic limitations, but (largely) reflects thermodynamics. The large-scale 2D phase separation in the monolayer islands can hardly be compared with the present calculations due to the unknown composition of the original surface layer. Our calculations only covered the case of a surface layer on one or two Ag sublayers (see above), which is likely not the case in those experiments. Comparing the present results of a tendency towards monolayer surface phase separation with those reported by Hua et al., they do not seem to agree, since these authors arrived at high Pt1 monomer surface concentrations for Pt/Ag(111) systems with low Pt bulk concentrations (<8%). In a more detailed look one has to keep in mind, however, that their simulation results were obtained for rather high temperatures, under dissolution -surface segregation equilibrium conditions, where phase separation is entropically disfavored. Furthermore, the formation of Pt1 surface monomers was supported by CO adsorption, which, as will be shown in section 3.3, is strongest on Pt1 monomers. Considering these aspects, there is no discrepancy to the present results for formation enthalpies and surface energies.