Efficient First-Principles Framework for Overdamped Phonon Dynamics and Anharmonic Electron-Phonon Coupling in Superionic Materials

TL;DR

This paper presents a new ab initio framework that accurately models overdamped phonon dynamics and electron-phonon interactions in superionic materials, capturing disorder and anharmonic effects efficiently.

Contribution

The authors develop an anharmonic special displacement method-based quasistatic framework for superionic conductors, enabling detailed electronic and vibrational property calculations.

Findings

Overdamped anharmonic vibrations in Cu2Se match experimental observations.

Polymorphism causes significant band gap openings and narrowing with temperature.

The method allows efficient electronic structure calculations in superionic crystals.

Abstract

Relying on the anharmonic special displacement method, we introduce an ab initio quasistatic polymorphous framework to describe local disorder, anharmonicity, and electron-phonon coupling in superionic conductors. Using the example of cubic Cu2Se, we show that positional polymorphism yields extremely overdamped anharmonic vibrations while preserving transverse acoustic phonons, consistent with experiments. We also demonstrate well-defined electronic band structures with large band gap openings due to polymorphism of 1.0 eV and calculate anharmonic electron-phonon renormalization, yielding band gap narrowing with increasing temperature in agreement with previous measurements. Our approach opens the way for efficient ab initio electronic structure calculations in superionic crystals to elucidate their compelling high figure-of-merit.