Predominance of non-adiabatic effects in zero-point renormalization of the electronic band gap

TL;DR

This paper demonstrates that non-adiabatic effects are crucial in accurately calculating zero-point band-gap renormalization, especially for light-element and infrared-active materials, challenging the traditional adiabatic approximation.

Contribution

It provides a large-scale first-principles analysis showing non-adiabatic effects often dominate zero-point band-gap renormalization, with a generalized Fröhlich model validated against these results.

Findings

Band gap renormalization exceeds 0.3 eV for light elements.

Non-adiabatic effects are essential for matching experimental data.

A generalized Fröhlich model accurately describes the effects.

Abstract

Electronic and optical properties of materials are affected by atomic motion through the electron-phonon interaction: not only band gaps change with temperature, but even at absolute zero temperature, zero-point motion causes band-gap renormalization. We present a large-scale first-principles evaluation of the zero-point renormalization of band edges beyond the adiabatic approximation. For materials with light elements, the band gap renormalization is often larger than 0.3 eV, and up to 0.7 eV. This effect cannot be ignored if accurate band gaps are sought. For infrared-active materials, global agreement with available experimental data is obtained only when non-adiabatic effects are taken into account. They even dominate zero-point renormalization for many materials, as shown by a generalized Fr\"ohlich model that includes multiple phonon branches, anisotropic and degenerate electronic extrema, whose range of validity is established by comparison with first-principles results.