Cohesive, structural, and electronic properties of Fe-Si compounds

Phase stability, structural, and electronic properties of iron silicides in the Fe3Si, FeSi, and FeSi2 compositions are investigated by first-principle density-functional calculations based on ultrasoft pseudopotentials and all-electron methods. Structural stabilization versus spin-polarization effects are discussed at the Fe3Si composition, while for epsilon-FeSi and beta-FeSi2 we investigate their structural properties and the corresponding semiconducting band properties. All the computed results are analyzed and compared to available experimental data. The stability of the bulk phases, the lattice parameters, the cohesive energies and magnetic properties are found to be in good agreement with experiment when using the generalized gradient approximations for the exchange-correlation functional. Density-functional calculations are unable to account for the small bulk modulus of epsilon-FeSi despite that the computed lattice constant and internal atomic positions coincide with the experimental results. Both full-potential and ultrasoft-pseudopotential methods confirm for beta-FeSi2 the indirect nature of the fundamental gap, which is attributed to a transition between Y to 0.6X Lambda being 30% smaller than the experimental gap. Ultrasoft pseudopotential calculations of Fe-Si magnetic phases and of various nonequilibrium metallic phases at the FeSi and FeSi2 composition are presented. These calculations provide nb initio information concerning the stabilization of metallic pseudomorphic phases via high pressures or epitaxy. [S0163-1829(99)05419-3].