Electron-phonon couplings in polymorphous crystals

TL;DR

This paper introduces a generalized ab initio method to accurately model electron-phonon interactions in polymorphous crystals, addressing longstanding issues in hybrid halide perovskite physics and linking local disorder to electronic properties.

Contribution

It extends the special displacement method to polymorphous systems, enabling efficient electron-phonon coupling calculations without molecular dynamics.

Findings

Resolved discrepancies in hybrid halide perovskite band gaps and phonons.

Linked local disorder and configurational entropy to electronic properties.

Provided a versatile approach applicable to various material classes.

Abstract

Positional polymorphism in solids refers to locally disordered unit cells that, on average, reproduce the high-symmetry structures observed in diffraction experiments. Standard theories of electron-phonon interactions fail to describe the temperature-dependent electronic structure of such polymorphous systems. Hybrid halide perovskites are a prime example, where configurational entropy from both polymorphism and molecular disorder plays a central role. Here we generalize the special displacement method to polymorphous crystals, providing an efficient ab initio framework for electron-phonon couplings without resorting to molecular dynamics. We resolve long-standing discrepancies in hybrid halide perovskite physics, including temperature-dependent anharmonic phonons and band gaps. Our approach provides a practical route to link local disorder, configurational entropy, and electron-phonon interactions, with applicability across diverse material classes, from optoelectronics and ferroelectrics to thermoelectrics.