First-Principles Phonon Quasiparticle Theory Applied to a Strongly Anharmonic Halide Perovskite

TL;DR

This paper introduces a first-principles quasiparticle phonon theory that accurately predicts lattice dynamics and phase transition temperatures in strongly anharmonic halide perovskites, surpassing traditional methods.

Contribution

The authors develop a novel first-principles approach incorporating bubble self-energy effects to improve phonon spectrum predictions in strongly anharmonic materials.

Findings

Accurately predicts the phase transition temperature of CsPbBr3.

Provides detailed phonon linewidth and quasiparticle peak information.

Shows significant improvement over conventional self-consistent phonon theory.

Abstract

Understanding and predicting lattice dynamics in strongly anharmonic crystals is one of the long-standing challenges in condensed matter physics. Here we propose a first-principles method that gives accurate quasiparticle (QP) peaks of the phonon spectrum with strong anharmonic broadening. On top of the conventional first-order self-consistent phonon (SC1) dynamical matrix, the proposed method incorporates frequency renormalization effects by the bubble self-energy within the QP approximation. We apply the developed methodology to the strongly anharmonic $\alpha$-CsPbBr$_3$ that displays phonon instability within the harmonic approximation in the whole Brillouin zone. While the SC1 theory significantly underestimates the cubic-to-tetragonal phase transition temperature (\tc) by more than 50\%, we show that our approach yields \tc = 404--423~K, in excellent agreement with the experimental value of 403~K. We also demonstrate that an accurate determination of QP peaks is paramount for quantitative prediction and elucidation of phonon linewidth..