Hydrogen induced surface metallization of $beta$-SiC(100)-($3times 2$) revisited by DFT calculations

Recent experiments on the silicon terminated $3times 2$ SiC(100) surface indicated an unexpected metallic character upon hydrogen adsorption. This effect was attributed to the bonding of hydrogen to a row of Si atoms and to the stabilization of a neighboring dangling bond row. Here, on the basis of Density-Functional calculations, we show that multiple-layer adsorption of H at the reconstructed surface is compatible with a different geometry: besides saturating the topmost Si dangling bonds, H atoms are adsorbed at rather unusual sites, textit{i.e.} stable bridge positions above third-layer Si dimers. The results thus suggest an alternative interpretation for the electronic structure of the metallic surface