Ab initio calculations of BaTiO₃ and PbTiO₃ (001) and (011) surface structures

We present and discuss the results of calculations of surface relaxations and rumplings for the (001) and (011) surfaces of BaTiO₃ and PbTiO₃ using a hybrid B3PW description of exchange and correlation. On the (001) surfaces, we consider both AO (A=Ba or Pb) and TiO₂ terminations. In the former case, the surface AO layer is found to relax inward for both materials, while outward relaxations of all atoms in the second layer are found at both kinds of (001) terminations and for both materials. The surface relaxation energies of BaO and TiO₂ terminations on BaTiO₃ (001) are found to be comparable, as are those of PbO and TiO₂ on PbTiO₃ (001), although in both cases the relaxation energy is slightly larger for the TiO₂ termination. As for the (011) surfaces, we consider three types of surfaces, terminating on a TiO layer, a Ba or Pb layer, or an O layer. Here, the relaxation energies are much larger for the TiO-terminated surface than for the Ba- or Pb-terminated surfaces. The relaxed surface energy for the O-terminated surface is about the same as the corresponding average of the TiO- and Pb-terminated surfaces on PbTiO₃, but much less than the average of the TiO- and Ba-terminated surfaces on BaTiO₃. We predict a considerable increase of the Ti-O chemical bond covalency near the BaTiO₃ and PbTiO₃ (011) surfaces as compared to both the bulk and the (001) surface.

©2007 The American Physical Society