U parameter of the Mott-Hubbard insulator 6H-SiC(0001)-(root 3 x root 3)R30 degrees: An ab initio calculation

The 6H-SiC(0001)-(root 3 X root 3)R30 degrees surface exhibits one half-fil led localized dangling-bond orbital per surface unit cell. Its electronic s tructure can accurately be described as a Mott-Hubbard insulator. We invest igate its spectrum by a spin-polarized ab initio quasiparticle calculation. The resulting band structure shows one occupied and one empty surface band , separated by a direct band gap of 1.95 eV. Since the band gap in the spec trum of the Hubbard model is directly given by the on-site Coulomb-interact ion parameter U of the dangling-bond orbital, our results allow for a relia ble determination of U = 1.95 eV.