It was shown that a (√3 x √3 ) buckling distortion with one raised and two lowered surface atoms per unit cell lowers by as much as 0.18eV/(surface atom) the energy of the clean, unreconstructed Si(111) surface. On the defect-free surface this state was not a true energy minimum, and was unstable against conversion into the lower energy (2 x 1) π-bonded chain reconstruction. A low concentration of added surface vacancies, however, was found to yield a buckled (√3 x √3 ) state which was a stable local minimum. Predictions were made for possible scanning-tunnelling-microscopy observation of this displacive reconstruction.

Theory of Vacancy-Stabilized (√3 x √3) Displacive Reconstruction of the Clean Si(111) Surface. F.Ancilotto, A.Selloni, E.Tosatti: Physical Review B, 1991, 43, 14726-9