The Si (100) surface—further studies of the pairing model

The potential, charge density, spectrum, and surface density of states is calculated self-consistently for the pairing-model reconstruction of the Si 2 1 (100) surface. This calculation differs from our earlier study in two ways. First, the pair bond has been contracted by 0. 13, keeping the back bonds equal to the bulk bonds (2. 35) in length. This change allows us to study how the pair bond spectrum and charge density depend on bond length and to discuss the forces driving and opposing the bond tightening. Secondly, the matching plane (behind which the potential is equal to the bulk potential) has been moved two atomic planes further into the crystal. There is little effect on the charge density in the back region, which allows us to verify that the thinner surface region used in the earlier calculation was sufficiently thick. The present study further strengthens our conclusion that the (100) silicon surface reconstructs to the 2 1 form by pairing.