Electronic structure and bonding of Si{100} surfaces

By arguments based on chemical-bond theory we have concluded that the structure of the {100} surfaces of Si involves asymmetrical pairs of a tricovalent Si^-(s²p³) atom and a tricovalent Si⁺(sp²) atom, with ideal bond angles 90^∘{} and 120^∘{}, respectively. With the minimizing of the sum of the squares of the deviations of the bond angles of these atoms and the atoms in the layer below from the ideal values (109.47^∘{} for the tetracovalent atoms in the layer below) the positional coordinates are assigned values close to those reported by Chadi and in rough agreement with experiment. The treatment leads also to a decision among alternative superstructures.