We are now focusing on one particular metal atom in the surface of a bimetallic surface, and thus on the local density of states (DOS) at that atom. Imagine that the surface layer is under compressive strain. This can for example be achieved by the pseudomorphic growth of a metal layer on a substrate with a smaller lattice constant . Alternatively, an effective compressive strain can also be produced by embedding the metal atom in a surface alloy layer with a fixed overall lattice, where the other metal species has a larger atom size. These geometric effects (strain effects) lead to an increased overlap of the metal orbitals, which results in a larger local band width (see Figure ), similar to the increased splitting between bonding and antibonding orbitals in molecular chemistry with increased overlap. Of course, there are also situations in which the d-band width becomes smaller, for example due to tensile strain, weaker interaction with neighbors. In this case, the d-band center of a late transition metal shifts upwards, leading to a stronger metal-adsorbate bond.