Non-Nominal Value of the Dynamical Effective Charge in Alkaline-Earth Oxides

TL;DR

This study uses ab-initio calculations to analyze the Born dynamical charge in alkaline-earth oxides, revealing deviations from nominal values due to orbital interactions and covalence effects.

Contribution

It provides a detailed band-by-band analysis of the dynamical charge trends and introduces computational experiments with artificial materials to understand covalence effects.

Findings

Z* increases along the series due to orbital interactions

Deviations from nominal charge are linked to O 2p and cation d state interactions

Variations in contributions are explained by occupied band manifolds

Abstract

We calculate ab-initio the electronic states and the Born dynamical charge Z* of the alkaline-earth oxides in the local-density approximation. We investigate the trend of increasing Z* values through the series, using band-by-band decompositions and computational experiments performed on fake materials with artificially-modified covalence. The deviations of Z* from the nominal value 2 are due to the increasing interaction between O 2p orbitals and unoccupied cation d states. We also explain the variations, along the series, of the individual contributions to Z* arising from the occupied band manifolds.