Facile ab initio approach for self-localized polarons from canonical transformations

TL;DR

This paper introduces a computationally efficient ab initio method based on canonical transformations to predict small polaron formation and energetics in materials, facilitating studies of charge localization.

Contribution

The authors develop a low-cost formalism using canonical transformations to accurately compute polaron energies and wavefunctions from first principles.

Findings

Successfully applied to alkali halides, metal oxides, and peroxides.

Enables determination of charge carrier localization tendencies.

Provides a foundation for future transport property calculations.

Abstract

Electronic states in a crystal can localize due to strong electron-phonon (e-ph) interactions, forming so-called small polarons. Methods to predict the formation and energetics of small polarons are either computationally costly or not geared toward quantitative predictions. Here we show a formalism based on canonical transformations to compute the polaron formation energy and wavefunction using ab initio e-ph interactions. Comparison of the calculated polaron and band edge energies allows us to determine whether charge carriers in a material favor a localized small polaron over a delocalized Bloch state. Due to its low computational cost, our approach enables efficient studies of the formation and energetics of small polarons, as we demonstrate by investigating electron and hole polaron formation in alkali halides and metal oxides and peroxides. We outline refinements of our scheme and extensions to compute transport in the polaron hopping regime.