Coulomb Correlations and Orbital Polarization in the Metal Insulator Transition of VO₂

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.