Coulomb Correlations and Orbital Polarization in the Metal Insulator Transition of VO_2

The quasi-particle spectra in the metallic rutile and insulating monoclinic phases of VO${}_2$ are shown to be dominated by local Coulomb interactions. In the rutile phase the small orbital polarization among V 3d t_2g states leads to weak static but strong dynamical correlations. In the monoclinic phase the large 3d orbital polarization caused by the V–V Peierls distortion gives rise to strong static correlations which are shown to be the primary cause of the insulating behavior.