First-principles total energy calculations were used to investigate adatom vacancies on the (111) 7 x 7 surface. In marked contrast to previous experimental estimates, the vacancy formation energies were estimated to have an average value of 0.9eV, with variations of the order of 0.1eV; depending upon the type of adatom. It was found that faulted or corner adatoms could be removed more easily than could unfaulted or edge adatoms, respectively. Structural relaxations caused large changes in the electronic structures of the surface states. Calculated scanning tunnelling microscopic images showed that the predicted variations could be expected to be easily observed by means of differential scanning tunnelling microscopic measurements.

Ab initio Studies of Adatom Vacancies on the Si(111)-(7×7) Surface. H.Lim, K.Cho, R.B.Capaz, J.D.Joannopoulos, K.D.Brommer, B.E.Larson: Physical Review B, 1996, 53[23], 15421-4