Ab initio lattice thermal conductivity of MgSiO3 across the perovskite-postperovskite phase transition

Lattice thermal conductivity (${\ensuremath{\kappa}}_{\mathrm{lat}}$) of $\mathrm{Mg}\mathrm{Si}{\mathrm{O}}₃$ postperovskite (MgPPv) under the Earth's lower mantle high pressure-temperature conditions is studied using the phonon quasiparticle approach by combing ab initio molecular dynamics and lattice dynamics simulations. Phonon lifetimes are extracted from the phonon quasiparticle calculations, and the phonon group velocities are computed from the anharmonic phonon dispersions, which, in principle, capture full anharmonicity. It is found that throughout the lowermost mantle, including the D'' region, ${\ensuremath{\kappa}}_{\mathrm{lat}}$ of MgPPv is \ensuremath{\sim}25% larger than that of $\mathrm{Mg}\mathrm{Si}{\mathrm{O}}₃$ perovskite (MgPv), mainly due to MgPPv's higher phonon velocities. Such a difference in phonon velocities between the two phases originates in the MgPPv's relatively smaller primitive cell. Systematic results of temperature and pressure dependences of both MgPPv's and MgPv's ${\ensuremath{\kappa}}_{\mathrm{lat}}$ are demonstrated.