We introduce a method for treating soft modes within the analytical framework of the quasiharmonic equation of state. The corresponding double-well energy-displacement relation is fitted to a functional form that is harmonic in both the lowand high-energy limits. Using density-functional calculations and statistical physics, we apply the quasiharmonic methodology to solid periclase ~MgO!. We pr...

We combine first-principles calculations of forces with the direct nonequilibrium molecular dynamics method to determine the lattice thermal conductivity k of periclase (MgO) up to conditions representative of the Earth's core-mantle boundary (136 GPa, 4100 K). We predict the logarithmic density derivative a=(∂ln k/∂ln ρ)(T)=4.6±1.2 and that k=20±5  Wm(-1) K(-1) at the core-mantle boundary, whi...

S U M M A R Y We develop a self-consistent thermodynamic description of silicate liquids applicable across the entire mantle pressure and temperature regime. The description combines the finite strain free energy expansion with an account of the temperature dependence of liquid properties into a single fundamental relation, while honouring the expected limiting behaviour at large volume and hig...

Ab initio thermodynamic properties, equation of state and phase stability of periclase (MgO, B1-type structure) have been investigated in a broad P–T range (0–160 GPa; 0–3000 K) in order to set a model reference system for phase equilibria simulations under deep Earth conditions. Phonon dispersion calculations performed on large supercells using the finite displacement method and in the framewo...

A multianvil apparatus ha been used to determine th pressure-temperature mel ing curve of forsterite from 9.7 to 16.5 GPa. At 10.1 GPa a singular point occurs that marks the change from congruent melting at lower pressures to incongruent melting (forsterite periclase + liquid) at higher pressures. The melting curve also passes through two invariant points. At one (15.6 GPa, 2310øC), the phases ...

[1] Knowledge of the elastic properties and crystal chemistry of dense oxide structures plays an important role in interpreting the composition and mineralogy of planetary interiors. We report the effects of (Mg,Fe) substitution and nonstoichiometry due to Fe on the crystal structure, elastic constants (cij) and moduli (K0T, K0S, G0) of (Mg,Fe)O utilizing single-crystal X-ray diffraction and gi...