First-principles study of surface segregation in Cu-Ni alloys

A method coupling electronic structure calculations with Monte Carlo simulations has been developed to determine surface compositions in Cu-Ni alloys. The calculations are based on an effective Ising model with parameters as defined within the framework of the generalized perturbation method and as calculated by means of the tight-binding version of the linear-muffin-tin-orbital method. Properties of Cu-Ni bulk alloys are discussed in terms of bulk effective interatomic interactions. The composition profiles are obtained for the fcc (001) surface for three bulk compositions, namely, Cu₇₅{Ni}₂₅$, ${Cu}₅₀Ni₅₀, and Cu₂₅{Ni}₇₅$. The major role played by the layer-dependent site-diagonal terms in the Ising model is emphasized. Our results are found to be in agreement with available experimental data.