Structure of the α-Cr₂O₃ (0001) surface: An ab initio total-energy study

The structure of the basal plane of the α phase of Cr₂O₃ has been investigated using periodic ab initio Hartree-Fock theory. The Cr-terminated surface, which is nonpolar but is charged, is found to be stable. However, a large-scale relaxation of the surface layer away from the ideal bulk-terminated structure has been found. The top layer Cr³⁺ ions move inward toward the second-layer O^2- ions by nearly 50% of their original interlayer spacing. This results in a slight lowering of the Cr ionicity in the surface layer, but no large-scale changes in bond character have been found. We therefore propose that the mechanism behind this dramatic reconstruction is purely electrostatic in origin. © 1996 The American Physical Society.