Breakdown of Minimal Mean Free Path Theory in MgSiO3 Perovskite*

Understanding the lattice thermal conductivity at high temperatures is important for many applications. We characterize phonon quasiparticles numerically through a hybrid approach that combines ab initio molecular dynamics and lattice dynamics. We find no lower-bound limits on
phonon mean free paths in MgSiO3-perovskite. This contradicts the widely used minimal mean free path idea. The clear identification of phonon quasiparticles validates the use of the phonon gas model when phonon mean free paths are shorter than lattice constants of solids. Using the phonon quasiparticle properties, we have calculated the lattice thermal conductivity of MgSiO3 perovskite, a controversial topic of fundamental importance in geophysics.