First-principles computation of the Born effective charges and their band-by-band decomposition

TL;DR

This paper explores first-principles methods for calculating Born effective charges in solids, analyzing different computational expressions and their band-by-band decompositions to understand their physical significance.

Contribution

It clarifies the connections between various computational approaches for Z* and highlights the physical meaning of a specific band-by-band decomposition.

Findings

Different expressions for Z* are connected but not equivalent in band decomposition.

One band-by-band decomposition has a meaningful physical interpretation.

The study enhances microscopic understanding of bonding in solids.

Abstract

The Born effective charge, Z*, that describes the polarization created by collective atomic displacements, can be computed from first-principles by different techniques. Its band-by-band decomposition appeared recently as a powerful tool for the microscopic characterisation of the bonding in solids. We describe the connections between the different expressions used for the computation of Z*, and analyze the possible associated band-by-band decompositions. We show that unlike for the full Z*, the different band-by-band values are not equal, and emphasize that one of them has an interesting physical meaning.