A study was made of the structural, electronic and magnetic properties of vacancy-bearing silicate mineral, Fe2SiO4 using first-principles density-functional theory. The simulated structure, which was compositionally close to naturally occurring laihunite, exhibited good agreement with general trends in the change in Fe2SiO4 crystal structure resulting from vacancy introduction. The study showed that the introduction of a vacancy created a charge disproportionation of Fe ions into Fe2+-like and Fe3+-like ions, with a charge difference greater than 0.5; the valences of the other ions being unaltered. The Fe2+-like ions were found to occupy octahedral sites of specific symmetry while the Fe3+-like ions occupied the other; leading to charge ordering at zero temperature.

First-Principles Simulations of Structural, Electronic, and Magnetic Properties of Vacancy-Bearing Fe Silicates. S.Chatterjee, T.Saha-Dasgupta: Physical Review B, 2010, 81[15], 155105