In addition, structural effects, e.g., the requirement of a certain minimum ensemble size (ensemble effects), may also play a role. shift with increasing number of Pt neighbors. Hence, while we expect strain effects to be of comparable magnitude for Pt and Pd based on their rather similar lattice parameters (3.9231 Å and 3.8898 Å, respectively ), ligand effects seem to be considerably stronger for PtAg/Pt(111) surface alloys than for PdAg/Pd(111) surface alloys. They dominate the modification in the electronic structure and thus also in the adsorption strength. Possible physical reason for that discrepancy are currently investigated in more detail.