Metal-insulator Transition in VO2: a DFT+DMFT perspective

In this Letter we present a theoretical investigation of the electronic structure of rutile (metallic) and monoclinic (insulating) phases of VO2 employing a fully self-consistent combination of density functional theory and embedded real space cluster-dynamical mean field theory calculations. We successfully describe the electronic structure of the metallic and both insulating phases of VO2 close to the metal-insulator transition and we propose a distinct mechanism for the gap opening. We show that Mott physics plays an essential role in all phases of VO2: undimerized vanadium atoms undergo classical Mott transition through local moment formation (in the M2 phase), while strong superexchange within V-dimers adds significant dynamic intersite correlations, which remove the singularity of self-energy for these V-atoms. The resulting transition from rutile to dimerized M1 phase is adiabatically connected to Peierls-like transition, but is better characterized as the Mott transition in the presence of strong intersite exchange. As a consequence of such Mott physics, the gap in the dimerized M1 phase is temperature dependent and we show that sole increase of electronic temperature collapses the gap, reminiscent of recent experiments.