Static structure, microscopic dynamics and electronic properties of the Fe–Ni and Fe–Ni–S liquid alloys. An <i>ab initio</i> molecular dynamics study

alloys which have both geophysical and technological (Invar alloys) interest. The motivation is twofold: first, to provide a first-principles description of atomic-scale structure and dynamics in these alloys, for which experimental data on some transport properties remain scarce; and second, to investigate the influence of sulfur on the local order, collective excitations, and viscosity. The calculated total static structure factors show excellent agreement with available neutron scattering (NS) experiments, validating the fidelity of the simulations. Self-diffusion coefficients for Fe and Ni in the binary alloys are found to be nearly identical and in good agreement with quasielastic NS data; the addition of sulfur substantially enhances diffusivity and reduces viscosity. The collective dynamics exhibit propagating acoustic modes, from which adiabatic sound velocities are derived. Analysis of transverse current correlation spectra uncovers, for the first time, the emergence of three distinct transverse branches in the dispersion relation of the minority Ni component at low wavevectors; this is a phenomenon not previously observed in liquid metals and prompts further theoretical investigation. The electronic density of states confirms metallic behavior and provides evidence of S(3p)-Fe(3d) hybridization.