First-principles potentials in modeling structure and thermodynamics of Fe-Ni alloys

First-principles local-density-functional (LD) calculations on small clusters were used to construct interaction potentials for iron and iron-nickel systems. The effective pair potential φᵢⱼ of the semiempirical embedded-atom method (EAM) was adopted for Ni-Fe and Fe-Fe interactions using differences: {Δ}φLD={Δ}φEAM and the Ni-Ni potential of Daw et al. The density-dependent embedding-energy function F({ρ}) of Fe was adjusted to conform to known scaling laws. The calculation of LD pair potentials was carried out for a number of Feₘ{Ni}ₙ$ clusters to determine suitable procedures for extracting {φ}. The effective potentials thus determined were applied to bulk and Fe-Ni alloys in molecular-dynamics simulations to determine equilibrium surface and bulk structures, and thermodynamical properties. The calculated bulk properties of Ni satisfactorily reproduce previous simulation results and experiment; those of bcc iron agree fairly well with experimental results. Moreover, certain properties such as vacancy-formation enthalpies are sufficiently sensitive to be useful in guiding further refinement of the potential.