A pair of partially occupied surface-state bands found in calculations of the 2 x 1 reconstructed Si(100) surface was shown to provide a mechanism for additional reconstruction via charge-density-wave formation. This was used as the explanation of weak 4th-order reflections seen in low-energy electron diffraction.

Secondary Reconstruction on the Si(100) Surface via a Charge-Density Wave. J.A.Appelbaum, G.A.Baraff, D.R.Hamann: Physical Review Letters, 1976, 36, 450-2. See also: Si(100) Surface Reconstruction - Spectroscopic Selection of a Structural Model. J.A.Appelbaum, G.A.Baraff, D.R.Hamann: Physical Review Letters, 1975, 35, 729-32