Barabash et al. had proposed to determine the (slab) formation energy Ef,slab of a bimetallic surface region using the pure substrate as reference. It describes the change in slab energy from the initial monometallic slab (Eslab,in) upon exchange of ni atoms of species i to/from a reservoir of that respective species to the final bi-or multicomponent slab and can be calculated via eq. ( )