Lattice-gas analog of density-functional theory: Application to ordering transitions

An alternative approach to ordering transitions in lattice gases is presented. Our approach can be regarded as the lattice analog of the well-known freezing theory for continuous fluids based on density functionals. Specifically, we discuss ordering in a three-dimensional model involving repulsive forces up to second neighbors and compare our results with Monte Carlo simulations. The utility of our method is demonstrated further by calculating the structure of a planar interface between coexisting ordered and disordered phases. It is pointed out that our theory is a good starting point for investigating problems of the interfacial kinetics.