Lattice Thermal Conductivity of MgSiO3 Postperovskite Under the Lowermost Mantle Conditions From Ab Initio Anharmonic Lattice Dynamics

The lattice thermal conductivity (κlat) of MgSiO3 postperovskite (Mg‐PPv) under the lowermost mantle pressure (P) and temperature (T) conditions was calculated using density functional theory combining anharmonic lattice dynamics theory. The κlat of Mg‐PPv was found to be ~50% higher than that of MgSiO3 bridgmanite (Mg‐Brg) owing to the larger phonon group velocity and lifetime. The lateral variation in the core‐mantle boundary heat flux (qCMB) can be enhanced by the Brg‐PPv phase transition. We also found that the κlat along the c axis of Mg‐PPv is close to the conductivity of isotropic aggregate. This suggests that the effect of anisotropy in the κlat on qCMB would be minor if the transversely isotropic aggregate with the c axis vertical alignment, a potential source of seismic anisotropy in the D″ layer, is developed. Key Points We perform ab initio anharmonic lattice dynamics simulations of MgSiO3 postperovskite under the lowermost mantle conditions Lattice thermal conductivity of postperovskite substantially increases associated with phase transition from bridgmanite Effects of anisotropy in the lattice thermal conductivity of postperovskite on the core‐mantle boundary heat flux are minor