Metallic nature of the symmetric dimer model of Si(001)-(2×1)

The electronic band structures of both the symmetric dimer model (SDM) and the asymmetric dimer model (ADM) of the Si(001)-(2×{}1) surface are investigated within the GW quasiparticle approximation. One purpose is to resolve the issue whether the metallic character of the SDM resulting in local-density approximation is just an artifact of that approximation. Our calculations show that the GW quasiparticle band structure of the SDM is metallic, as well, in disagreement with experiment, whereas the results for the ADM nicely agree with the experimental data. These findings strongly support the notion that the Si(001)-(2×{}1) surface consists of asymmetric dimers.