From: Bernd Meyer <bemeyer@physics.rutgers.edu> Date: Wed, 20 Sep 2000 00:36:26 GMT (65kb)
Authors:
B. Meyer,
David Vanderbilt (Department of Physics and Astronomy, Rutgers University)
Comments: 10 pages, two-column style with 10 postscript figures embedded. Uses
REVTEX and epsf macros
Subj-class: Materials Science
For the ferroelectric perovskite compounds BaTiO3 and PbTiO3, we have studied the effects of external electric fields on the structural properties of the (001) surfaces. The field-induced changes in the surface interlayer spacings and bucklings have been calculated using a first-principles ultrasoft-pseudopotential approach, and the change of the polarization and the ferroelectric distortions in the surface layers have been obtained. The surfaces are represented by periodically repeated slabs, and an external dipole layer is included in the vacuum region of the supercells to impose an external electric field on the surfaces. This dipole layer is also used to compensate artificial electric fields introduced by the periodic repetition of the polarized slabs. The influence of the electrical boundary conditions on the ferroelectric properties of the slabs is discussed. We find that in the case of a vanishing internal electric field, the slabs show a ferroelectric instability down to very small thicknesses, with an enhancement or reduction of the polarization at the surface depending on the orientation of the spontaneous polarization.