General trend for adsorbate-induced segregation of subsurface metal atoms in bimetallic surfaces.

It is well known that the unique chemical properties of transition metal alloys depend on the configuration of metal atoms of the bimetallic surfaces. Using density functional theory calculations, the thermodynamic potential for segregation of an admetal from the subsurface to surface configuration is shown to correlate linearly with the difference in occupied d-band center, Delta epsilon(d), between these two configurations for a wide range of bimetallic systems. The thermodynamic potential for segregation is also shown to increase with the Pauling electronegativity for several adsorbates, including atomic H, O, C, N, S, and Se. A generalized equation is provided to predict the stable surface configuration for the bimetallic systems with different adsorbates.