  We present the first ab initio density functional theory study of the
oxygen-terminated Cr2O3 (0001) surface within the local spin-density
approximation (LSDA). We find that spin plays a critical role for even the most
basic properties of Cr2O3 such as the structure and mechanical response of the
bulk material. The surface exhibits strong relaxations and changes in
electronic and magnetic structure with important implications for the chemical
reactivity and unusual spin-dependent catalytic activity of the surface. Unlike
the bulk, the outermost chromium bilayer is ferromagnetically ordered, and the
surface oxygen layer exhibits appreciable net spin polarization in the opposite
sense. Surprisingly, despite this ferrimagnetic order, the chemically important
states near the Fermi level exhibit ferromagnetic order and thus favor
electronic spin alignment of species interacting with the surface. Finally, we
also find a high density of unoccupied electronic surface states available to
participate in the chemical reactivity of the surface.
