Comment on “Cluster expansion and the configurational theory of alloys”

Cluster expansions with concentration-independent interactions have been widely used to model the formation energies of alloys. In the Sanchez paper [Phys. Rev. B 81, 224202 (2010)], this practice is called into question based on the argument that a truncated cluster expansion with concentration-independent interactions cannot be used to represent the formation energy of a random alloy if the formation energy is a nonlinear function of concentration. To clarify the validity of using cluster expansions with concentration-independent interactions, I demonstrate that this argument is not necessarily correct.