Ab initio studies of opto-electronic excitations in VO2

We study the optical response of VO2 in the M1 insulating phase using methods based on density functional theory in its most recent developments. We start from a hybrid functional approach which may be a good starting point to carry out many-body perturbation theory since, as we show, it gives a qualitatively and to some degree quantitatively correct description of the insulating phase. In order to calculate the dielectric function, first, using hybrid density functional wavefunctions we have added GW corrections on top of the hybrid density functional calculations and we solved the so-called Bethe Salpeter equation to include effects of correlations of the electron-hole pair created upon photon absorption. We find that the effects of electron correlations are very important and they show up as a strong contribution of the electron-hole interaction in calculating the effects of the Bethe-Salpeter equation in the electron/hole pair excitation on top of the interacting group state.