Spin state of ferrous iron in perovskite

Diamond anvil cell experiments at pressures up to 145 GPa have shown evidence for a high spin to low spin transition in iron in magnesium silicate perovskite (MgSiO$_3$.) The spin transition will influence the optical absorption spectrum and elastic properties of this mineral. We present density functional calculations of (Mg,Fe)SiO$_3$ with ferrous iron substituting for magnesium at a concentration of 12.5\%. The calculations use the local density approximation with Hubbard term (LDA+U) and supercells containing up to 160 atoms. We describe the pressure dependence of the iron spin state. Research supported by NSF/EAR 0230319, NSF/ITR 0428774 and 0426757, VLab, NSF/ITR 0325218, ITAMIT.