First principles calculations of insulator-to-metal transition in photoexcited monoclinic VO2

The insulator-to-metal phase transition of VO2 has been discovered for a long time, but its origin remains elusive. In recent experiments, ultrafast band gap collapse of monoclinic VO2 upon photo excitation was observed through time resolved photoelectron spectroscopy (TRPES). In order to study this issue, we have performed first principles calculations based on many-body perturbation theory. We show that the band gap in monoclinic phase is extremely sensitive to small changes in the occupation of the localized d bands of V atoms. In particular, the photo-induced hole doping in VO2 can strongly alter the dynamical screening, which then leads to a collapse of the band gap. Our results support the experimental findings and point to the electronic origin of the insulator-to-metal phase transition of monoclinic VO2 in the TRPES experiments.