Thermodynamic properties of (Mg,Fe2+)SiO3 perovskite at the lower-mantle pressures and temperatures: an internally consistent LSDA+U study

摘要: SUMMARY The thermodynamic properties of (Mg0.9375Fe2+0.0625)SiO3 perovskite have been investigated at the pressure and temperature conditions lower mantle by first-principles calculations where iron is incorporated in high low-spin states for first time. The electronic structure ferrous Fe-bearing modelled within internally consistent local spin density approximation with a Hubbard correction U. are derived from calculation Helmholtz free energy quasi-harmonic approximation, which requires phonon frequencies determined direct dynamic matrices. Incorporation iron, irrespective its states, decreases acoustic mode frequencies, but less affects high-energy optic modes, leading to decreasing wave velocities MgSiO3 perovskite, previous studies on elasticity this phase. This study suggests that silicate such as equation state isothermal bulk modulus, not largely modified incorporation 6.25 per cent iron. Calculations static enthalpy iron-bearing 0–150-GPa-pressure range demonstrate unstable mantle. Finally, we clarify perovskite-to-post-perovskite phase transition boundary an (Mg0.9375Fe0.0625)SiO3 composition. Ferrous found decrease between two phases small binary loop 3–4 GPa lowermost 111 115 2500 K 116 119 3000 K.