First-principles simulations of structural, electronic, and magnetic properties of vacancy-bearing Fe silicates

Abstract

We study the structural, electronic, and magnetic properties of vacancy-bearing silicate mineral, Fe₂SiO₄ using first-principles density-functional theory (DFT). Our DFT-simulated structure, which is compositionally close to naturally occurring laihunite compound shows good agreement in the general trend in the change in Fe₂SiO₄ crystal structure upon vacancy introduction. Our study shows that the introduction of vacancy creates charge disproportionation of Fe ions into Fe²⁺-like and Fe³⁺-like ions with a charge difference larger than 0.5, keeping the valences of other ions unaltered. Fe²⁺-like ions are found to occupy octahedral sites of specific symmetry while Fe³⁺-like occupy the other leading to charge ordering at zero temperature. We also study the magnetic ordering of Fe ions.