AB-INITIO TOTAL-ENERGY STUDIES OF THE ALPHA-CR2O3(0001) AND ALPHA-CR2O3(01(1)OVER-BAR-2) SURFACES

The surface structure of the basal plane and of the thermodynamically most stable facet of the alpha phase of Cr2O3 has been studied using p eriodic ab initio Hartree-Fock theory. The Cr-terminated (0001) surfac e, which is nonpolar but charged, is found to be stable. However, a la rge scale relaxation of the surface layer away from the ideal bulk-ter minated structure has been found. The outermost layer of Cr3+ ions mov es inward toward the second layer of O2- ions by nearly 50% of their o riginal interlayer spacing. The (01(1) over bar 2) surface, which is o xygen-terminated, is also nonpolar, and stable. Again an appreciable r elaxation, with the top layer moving outward compared with the ideal b ulk structure, is found. The driving force behind both effects is pres umed to be mainly electrostatic.