Possibility of a Mott-Hubbard ground state for the SiC(0001) surface

The possibility that large electronic correlation effects produce a semiconducting surface-state spectrum for the $\mathrm{Si}{-T}_4$ adatom model of the $\mathrm{SiC}\mathrm{}\left(0001\right)\mathrm{}\sqrt{3}\times \sqrt{3}$ surface is discussed. We argue that a Hubbard model, with parameters obtained from local-density calculations, provides a qualitatively correct account of the excitation spectra inferred from angle-resolved photoemission and inverse-photoemission experiments. The Hubbard $U$ parameter obtained in local-density-functional calculations for the Si-adatom dangling bond on SiC(0001) is 1.6 eV.