A. Pojani et al., A THEORETICAL-STUDY OF THE STABILITY AND ELECTRONIC-STRUCTURE OF THE POLAR (111)-FACE OF MGO, Surface science, 387(1-3), 1997, pp. 354-370
The stability of the polar {111} face of MgO is discussed on the basis
of the results obtained by a total-energy semi-empirical Hartree-Fock
method, and on general theoretical arguments relying on a perturbativ
e approach of covalent effects in mixed iono-covalent solids. The idea
l stoichiometric (1 x 1) surface is studied and compared to two (2 x 1
) and (2 x 2) reconstructed surfaces, and to a fully hydroxylated (1 x
1) surface. On the ideal surface, a strong electron redistribution ta
kes place in order to cancel the polarity, which is associated with a
metallization of the surface layers and with a high surface energy. A
spontaneous symmetry breaking of the Peierls type takes place on this
surface, with an opening: of a gap at the Fermi level which induces a
desorption of half of the surface atoms and a (2 x 1) reconstructed su
rface configuration. On the two reconstructed surfaces the modificatio
n of the stoichiometry in the surface layers provides the compensating
charges. As a result, they are much more stable and insulating. The (
2 x 2) reconstruction which involves nanopyramids with {001} facets is
favored, but we predict a trend to form larger facets in (2n x 2n) re
constructions. (C) 1997 Elsevier Science B.V.