Correlation Assisted Phonon Softenings and the Mott-Peierls Transition in VO$_{2}$

TL;DR

This study investigates the phonon behaviors in VO2 using DFT and DFT+U calculations, revealing the essential role of Coulomb correlation in the metal-insulator and structural transitions, and predicting a new high-pressure phase.

Contribution

It demonstrates that Coulomb correlation assists the Peierls transition in VO2 and predicts a new high-pressure metallic phase with a monoclinic CaCl2-type structure.

Findings

Phonon softening occurs in both DFT and DFT+U calculations.

Only DFT+U accurately describes the MIT and structural transition.

A new high-pressure phase of VO2 with metallic properties is predicted.

Abstract

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 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). This feature demonstrates that the Coulomb correlation effect plays an essential role of assisting the Peierls transition in R-VO2. We have also found from the phonon dispersion of M1-VO2 that M1 structure becomes unstable under high pressure. We have predicted a new phase of VO2 at high pressure that has a monoclinic CaCl2-type structure with metallic nature.