Lattice Thermal Conductivity of MgSiO 3 Postperovskite Under the Lowermost Mantle Conditions From Ab Initio Anharmonic Lattice Dynamics

The lattice thermal conductivity ( κ lat ) of MgSiO 3 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 κ lat of Mg‐PPv was found to be ~50% higher than that of MgSiO 3 bridgmanite (Mg‐Brg) owing to the larger phonon group velocity and lifetime. The lateral variation in the core‐mantle boundary heat flux ( q CMB ) can be enhanced by the Brg‐PPv phase transition. We also found that the κ lat along the c axis of Mg‐PPv is close to the conductivity of isotropic aggregate. This suggests that the effect of anisotropy in the κ lat on q CMB 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.