By using an ab initio plane-wave pseudopotential code, a study was made of various 3x1 and 3x2 reconstructions; including adatom (A), dimer (D) and interstitial (I) models of (113) surfaces. All reconstruction elements gave rise to local minima on the total-energy surface. Interstitial reconstructions were confirmed to be most favorable. Reconstructions without interstitials, even the oppositely puckered 3x2 AD model, did not open a surface-state gap. The 3x2 AI surface, with asymmetrical pentamers, was semiconducting and relatively low in energy. The measured structural data, the observed (in particular occupied) surface states, the scanning-tunneling microscopic images of Ge(113)-3x2 and 3x1 surfaces, as well as the temperature-induced phase transitions, could be largely explained by using models with sub-surface interstitial atoms and by accounting for the mobility of such atoms.

Adatoms, Dimers and Interstitials on Group-IV (113) Surfaces - First-Principles Studies of Energetic, Structural and Electronic Properties. A.A.Stekolnikov, J.Furthmüller, F.Bechstedt: Physical Review B, 2003, 67[19], 195332 (10pp)