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

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 α-CsPbBr3 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 lattice thermal conductivity.

Weak Anharmonicity Rationalizes the Temperature-Driven Acceleration of Nonradiative Dynamics in Cu2ZnSnS4Photoabsorbers

“…However, elevated temperatures do tend to induce largeamplitude atom displacements, which may lead to a breakdown of the harmonic phonon theory at a higher temperature due to anharmonicity. 56,57 This motivates us to quantify the vibrational anharmonicity of ks-CZTS at different temperatures. We compute the anharmonic score, σ A (T), which is defined as 43…”

Anharmonic lattice dynamics in large thermodynamic ensembles with machine-learning force fields: CsPbBr3 , a phonon liquid with Cs rattlers

“…1). It is reported to possess closely spaced phonon branches and overlapping linewidths [20,21], and highly anharmonic coupling between the atoms [22,23]. This makes this material a very interesting candidate to study the atomic vibrations in a framework with an accuracy beyond the harmonic approximation [6,[16][17][18]20,[24][25][26].…”