A comparative study of phonon anharmonicity and lattice thermal transport with perturbation theory and molecular dynamics

Phonon properties are crucial to determine the intrinsic lattice thermal transport of strongly anharmonic materials. Using the state-of-the-art perturbation theory (PT) including up to the fourth-order anharmonicity and molecular dynamics (MD) with accurate first-principles-based machine learning potential, we calculated the phonon lifetimes and lattice thermal conductivities of strongly anharmonic materials Tl₃VSe₄ and BaAg₂Te₂. We find that PT underestimates the phonon scatterings in the entire Brillouin zone for Tl₃VSe₄ and BaAg₂Te₂ at room temperature, and the calculated phonon lifetimes based on MD simulations show a better agreement with experimental results. Using unified theory on top of accurate phonon properties, we reveal a significant two-channel lattice thermal transport in these strongly anharmonic materials at high temperatures. Our results pave the avenue for future studies of phonon properties and ultralow lattice thermal conductivities of strongly anharmonic crystals beyond the conventional PT realm.