Hartree-Fock Studies of the Ferroelectric Perovskites

TL;DR

This paper uses Hartree-Fock calculations to study ferroelectric perovskites, comparing results with experiments and exploring surface properties of BaTiO_3, providing insights into electronic and dynamical characteristics.

Contribution

It applies ab-initio Hartree-Fock methods with Berry-phase and supercell calculations to analyze ferroelectric perovskites and their surfaces, highlighting differences from LDA and surface charge neutrality.

Findings

HF results are comparable to LDA in accuracy for electronic properties.

Significant differences between HF and LDA results are analyzed.

BaTiO_3 surfaces exhibit nontrivial dynamical-charge neutrality.

Abstract

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.