Composition, chemical disorder, and magnetism significantly affect the
volume and bulk modulus of iron–silicon (Fe–Si) alloys at ambient
pressure. Here, we computed the equations of state for bcc-like (ordered
B2 and disordered bcc) Fe–Si alloys available up to the inner-core
pressure using the first-principles Korringa–Kohn–Rostoker method.
Ferromagnetic (FM) and nonmagnetic (NM) states over a wide composition
range, from Fe to FeSi, were investigated. The results revealed that
magnetism and chemical disorder increased the volume and decreased the
bulk modulus even at high pressures. Comparing the results with the
preliminary reference Earth model, we found that an unrealistically
large temperature gradient is required if the inner core is composed of
a bcc-like Fe–Si alloy.