Surface effects in ferroelectrics: Periodic slab computations for BaTiO3

Total energies, electronic structure, surface energies, polarization, potentials and charge densities were studied for slabs of BaTiO3 using the Linearized Augmented Plane Wave (LAPW) method. The depolarization held inhibits ferroelectricity in the slabs, and the macroscopic field set up across a ferroelectric slab is sufficient to cause electronic states to span the gap and give a metallic band structure, but the band shifts are not rigid and O p states tend to pile up at the Fermi level. There are electronic surface states, especially evident on TiO2 surfaces. The dangling bonds bond back to the surface Ti's and make the surface stable and reactive. The BaO surfaces are more ionic than the bulk.