Surface, Interface, Compression and Formation Energies of Bimetallic Ag/Pt(111) and Ag/Pd(111) Surfaces from First-Principles

As an example for bimetallic surfaces in general, we have systematically investigated the thermodynamic surface properties of bimetallic Ag/Pt(111) and Ag/Pd(111) surfaces, including pseudomorphic Ag film covered surfaces and M1Ag3/M­(111) (M = Pt, Pd) monolayer surface alloys, by periodic density functional theory calculations. Employing larger, symmetric unit cells and slabs, we could determine the surface energy of the asymmetric surface region without interference with contributions from the bottom side of the slab used in these calculations. In the calculation of formation energies, we distinguish between bulk and slab formation energies. Interface energies are derived from appropriately structured bulk unit cells, and corrected for contributions arising from the compression of pseudomorphic film layers (compression energy). While the general trends for the Pt(111)- and Pd(111)-based systems are rather similar, we also find specific differences. Possible reasons for these trends and the specific discrepancies will be addressed. We propose that the procedures presented here are of general validity and can be applied also to other complex surfaces.