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Perturbation theories have been successful in calculating lattice dynamics with moderate anharmonicity,which is sufficient to reproduce lattice thermal conductivity of many crystals even at high temperatures.However,there are materials and cases,where stronger anharmonicity manifests itself in the phonon dynamics,and further understanding of their nature can lead us to better design and control of lattice heat conduction.We have recently investigated anharmonic phonon dynamics in crystals and their interfaces using classical molecular dynamics simulations with interatomic force constants obtained from first principles.The molecular dynamics method allows us to simulate anharmonic lattice dynamics with atom displacements beyond the limit of the perturbation theories.With this,we have identified the origin of anomalous anharmonic lattice dynamics of lead telluride previously observed in experiments.In addition,we have clarified the contribution of the inelastic phonon transmission to the thermal boundary conductance across bonded crystal interfaces.