Ab initio study of BaTiO3 and PbTiO3 surfaces in external electric fields - art. no. 205426

For the ferroelectric perovskite compounds BaTiO3 and PbTiO3, we have studi ed the effects of external electric fields on the structural properties of the (001) surfaces. The field-induced changes in the surface interlayer spa cings and bucklings have been calculated using a first-principles ultrasoft -pseudopotential approach, and the change of the polarization and the ferro electric distortions in the surface layers have been obtained. The surfaces are represented by periodically repeated slabs, and an external dipole lay er is included in the vacuum region of the supercells to control the electr ic field normal to the surfaces. The influence of the electrical boundary c onditions on the ferroelectric properties of the slabs is discussed. In the case of a vanishing internal electric field, our study indicates that even very thin slabs can show a ferroelectric instability.