Renormalized lattice dynamics and thermal transport of VO₂

Vanadium dioxide (VO₂) undergoes a first-order metal-insulator transition (MIT) upon cooling near room temperature. The MIT is concomitant with structural changes from rutile to monoclinic, and an accurate characterization of lattice vibrations is vital for elucidating the underlying phase transition mechanism. To investigate the lattice dynamics and thermal transport properties of VO₂ across the MIT, we demonstrate a phonon renormalization scheme based on self-consistent phonon theory through iteratively refining vibrational free energy. Using this technique, we compute temperature-dependent phonon dispersion and lifetime, identify extremely strong anharmonicity associated with low-lying zone-center optical mode, and point out the importance of both magnetic and vibrational entropy in driving MIT. We reveal that lattice thermal conductivity of rutile VO₂ is nearly temperature independent as a result of the strong intrinsic anharmonicity, while that of monoclinic VO₂ varies according to 1/T. Based on the good agreement between our predicted and experimentally measured phonon dispersion and lifetime, we will further comment on a recently identified strong violation of Wiedemann-Franz law in rutile VO₂.