Furthermore, also the neighbors of the respective adsorption ensemble, including both atoms directly aside and/or directly underneath the respective surface ensemble, may modify the adsorption properties of these sites by electronic interactions (ligand effects) or by imposing lattice strain (strain effects ). Thus, the concepts of the (geometrical) ensemble effect and the (electronic) ligand effect, which had been initially introduced in the discussion of the catalytic activity of bimetallic catalysts (see sections 1. and 3.2 as well as references ), are equally applicable also for the description of adsorption properties. In fact, these modifications of the adsorption properties provide the rational basis for the trends in the catalytic activity of these systems.