  Within an ab-initio HF scheme, we use both Berry-phase calculations and
supercell calculations in order to compute the dynamical charges for lattice
dynamics and the electronic dielectric constant for KNbO_3 and BaTiO_3.
Comparison with experimental data indicates that HF provides a description of
the electronic properties of this material whose accuracy is of the same order
as the LDA one. There are however significant differences between the two sets
of results, whose origin is scrutinized. Motivated by the study of surface and
domain-boundary properties, we also present some results for BaTiO_3 slabs,
including both genuinely isolated and periodically repeated slabs with
different terminations. The capability of dealing with a genuinely isolated
slab is a virtue of the localized-basis implementation adopted here. We
demonstrate, amongst other things, the nontrivial dynamical-charge neutrality
of BaTiO_3 [001] surfaces.
