Missing-Row Asymmetric-Dimer Reconstruction ofSiC(001)−c(4×2)

A new reconstruction model for the cubic $\mathrm{SiC}\left(001\right)-c(4\times 2)$ surface is suggested on the basis of ab initio pseudopotential total energy and grand canonical potential calculations. Our results clearly favor an adatom structure with half a monolayer of Si atoms adsorbed at the Si-terminated surface. The adatoms form a missing-row reconstruction with strong asymmetric dimers whose bond length is 2.3 Å. The model exhibits a semiconducting surface and it is in good accord with recent experimental data. The previously suggested alternatively up- and down-dimer model turns out to be neither a stable nor a metastable structure.