First-principles theory of frozen-ion flexoelectricity

TL;DR

This paper presents a first-principles theory for frozen-ion flexoelectricity, expressing it through charge density moments, and introduces practical computational methods validated on various materials.

Contribution

It provides a novel theoretical framework for calculating frozen-ion flexoelectric coefficients using charge density moments and offers practical supercell-based computational methods.

Findings

Derived a formula for frozen-ion flexoelectricity based on charge density moments.

Developed supercell-based computational methods for first-principles calculations.

Validated methods on materials like C, Si, MgO, NaCl, and perovskites.

Abstract

We demonstrate that the frozen-ion contribution to the flexoelectric coefficient is given solely in terms of the sum of third moments of the charge density distortions induced by atomic displacements, even for ferroelectric or piezoelectric materials. We introduce several practical supercell-based methods for calculating these coefficients from first principles, and demonstrate them by computing the coefficients for C, Si, MgO, NaCl, SrTiO$_3$, BaTiO$_3$, and PbTiO$_3$. Three important subtleties associated with pseudopotentials, the treatment of surfaces, and the calculation of transverse components are also discussed.