Two successive spin transitions in a wide range of pressure and coexistence of high- and low-spin states in clinoferrosilite FeSiO 3

We present a theoretical study of spectral and magnetic properties of clinoferrosilite ${\mathrm{FeSiO}}_{3}$. Within the DFT+DMFT method combining local density approximation with dynamical mean-field theory ${\mathrm{FeSiO}}_{3}$ was investigated in a wide range of pressure and temperature including the lower Earth's mantle conditions. For clinoferrosilite, which crystallizes in a monoclinic crystal structure, we predict two high-spin to low-spin transitions under pressure in the Fe-$3d$ shell with a crossover region at moderate temperatures, which becomes much broader at higher temperatures. An analysis of the Fe electronic configurations reveals that in clinoferrosilite the low- and high-spin states are predominantly involved and coexist in the spin crossover region, while a small amount of the intermediate spin states appears only at very high pressures and can be attributed to the distorted crystal structure of clinoferrosilite ${\mathrm{FeSiO}}_{3}$.