(2 × 1) reconstructed Si(001) surface: Self-consistent calculations of dimer models

The electronic structure of the (2 1) reconstructed Si (001) surface is studied using the self-consistent pseudopotential method. The calculation is based on the asymmetric-dimer model recently proposed by Chadi using the tight-binding method. The present calculation confirms that the asymmetric-dimer model results in a semiconducting surface in agreement with experiment. The density of states is calculated, and it compares favorably with experiment. A study of the charge distributions and the energy dispersions of surface states allows us to determine the character of individual surface states. By doing comparative calculations of the total energy of the symmetric and asymmetric dimers, we conclude that the latter is more stable because of exchange-correlation energy contributions.