Periodic slab LAPW computations for ferroelectric BaTiO3

Linearized augmented plane wave (LAPW) calculations are performed for periodic (001) and (111) slabs of BaTiO3 to understand the effects of surfaces on ferroelectric BaTiO3. The (111) slab is found to be much less stable than the (001) slab. The depolarization held is sufficiently large in the ideal unrelaxed slab to completely inhibit the ferroelectric instability. No mid-gap surface states are evident, but there are surface states in the upper gap in the unrelaxed slab and at the top of the valence band. The dangling surface Ti bonds self-heal making the Ti-O surface very reactive and an excellent epitaxial substrate. The charge density on atoms only one unit cell away from the surface are almost identical to the bulk.