Strong-correlation effects in Born effective charges

TL;DR

This paper investigates how strong electron correlation influences Born effective charges, revealing that such correlations reduce their magnitude and provide insights into their relation with electronic structure, challenging their use as sole indicators of ferroelectricity.

Contribution

It introduces a novel, self-interaction free methodology that improves electronic property calculations and systematically analyzes the impact of strong correlations on Born effective charges.

Findings

Strong correlations decrease Born effective charges.

Correlation effects reduce electron localization lengths.

Band structure and orbital occupations explain charge variations.

Abstract

Large values of Born effective charges are generally considered as reliable indicators of the genuine tendency of an insulator towards ferroelectric instability. However, these quantities can be very much influenced by strong electron correlation and metallic behavior, which are not exclusive properties of ferroelectric materials. In this paper we compare the Born effective charges of some prototypical ferroelectrics with those of magnetic, non-ferroelectric compounds using a novel, self-interaction free methodology that improves on the local-density approximation description of the electronic properties. We show that the inclusion of strong-correlation effects systermatically reduces the size of the Born effective charges and the electron localization lengths. Furthermore we give an interpretation of the Born effective charges in terms of band energy structure and orbital occupations which can be used as a guideline to rationalize their values in the general case.