Correlation-assisted phonon softening and the orbital-selective Peierls transition in VO₂

To explore the driving mechanisms of the metal-insulator transition (MIT) and the structural transition in VO₂, we have investigated phonon dispersions of rutile VO₂ (R-VO₂) in the density functional theory (DFT) and the DFT+U (U: Coulomb correlation) band calculations. We have found that the phonon softening instabilities occur in both cases, but the softened phonon mode only in the DFT+U describes properly both the MIT and the structural transition from R-VO₂ to monoclinic VO₂ (M₁-VO₂). The present ab initio phonon dispersion calculations clearly demonstrate that the Coulomb correlation effect plays an essential role of assisting the Peierls transition in R-VO₂ and producing the spin-Peierls ground state in M₁-VO₂.