Adatom vacancies on the Si(111)-(7 x 7) surface

The structures, energies and electronic properties of the adatom vacancies on the Si(111)-(7 x 7) surface are studied by tight-binding molecular dynam ics calculations using the recently developed environment-dependent potenti al of silicon. Adatom vacancies on the edge of the (7 x 7) unit cell are fo und to have formation energies lower than those on the corner of the unit c ell by about 0.1 eV. Structure relaxation induced by the vacancies is found to be significant. Localized electronic states associated with the vacanci es are also observed at energy about 0.5 eV below the Fermi energy level. ( C) 1999 Elsevier Science B.V. All rights reserved.