Effect of the surface polarization in polar perovskites studied from first principles

The (001) surfaces of polar perovskites BaTiO${}_3$ and PbTiO${}_3$ have been studied from first principles at T=0 K. For both cases of polarization, the most stable TiO-terminated interfaces show intrinsic ferroelectricity. In the topmost layer, where the O atoms are $>$0.1 \AA above Ti, this leads to metallic instead of the insulating behavior of the electronic states that may have important implications for multiferroic tunneling junctions.