The structural and electronic relaxation of the alpha-Al₂O₃ surface

P. Reinhardt

Université Paris VI, France

F. Illas, J.R.B. Gomes, I. de P.R.Moreira

Universitat de Barcelona, Spain

The geometrical structure of the polar, Al-terminated surface of corundum has been investigated by different theoretical methods ranging from empirical pair potenials to periodic Hartree-Fock or Density Functional Theory calculations. Qualitatively, all the methods agree on a large inward relaxation of the outermost Al layer and less pronounced differences from bulk position for the other Al positions. Significant differences occur, however, when regarding the results more closely; empirical potentials seem too crude for employing them in surface structure optimizations, and on the other hand we propose that the largest relaxations, observed from DFT calculations including pseudopotentials, are rather an artefact of the method than a physical effect. Another question addressed in the present contribution is the generation of a net dipole moment perpendicular to the relaxed surface. A simple ionic model may serve for explaining the presence of the dipole moment, and, of course, the direction of the observed geometrical relaxations. Charge polarization on the surface atoms in all-electron calculations is not enough to compensate the moment arising from the point-charge model.

Contact author:
Peter Reinhardt
Laboratoire de Chimie Théorique
Université Paris VI,
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F-75252 Paris CEDEX 05
France
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