Effect of anharmonicity and polymorphism on electron-phonon coupling in halide perovskites
Résumé
State-of-the-art electronic structure calculations for cubic halide perovskites areperformed by assuming that the potential energy felt by electrons is described withthe nuclei clamped at their crystallographic positions. This assumption inevitablymisses the effect of polymorphism and anharmonicity which are ubiquitous in thisclass of materials, affecting profoundly their mechanical stability, as well as theiroptoelectronic and light-absorbing properties. In this talk, I will uncover the importantrole of polymorphism and anharmonicity in the phonon dynamics and electronphononinteraction of cubic perovskites [1]. In particular, I will show that (i) latticedynamics in polymorphous halide perovskites depart severely from the textbookphonon picture, exhibiting overdamped vibrational dynamics, (ii) anharmonic opticalvibrations dominate electron-phonon coupling, and (iii) electronic structurecalculations of cubic perovskites require combined corrections due to polymorphism,spin-orbit coupling, functionals beyond density functional theory, and anharmonicelectron-phonon coupling. To address points (i)-(iii) we develop a new computationalapproach to anharmonicity relying on the special displacement method (A-SDM) [2].In this talk, I will also present the merits of A-SDM which opens up new avenues forvery efficient first-principles calculations in strongly anharmonic materials at finitetemperatures. I will demonstrate that only a couple of atomic configurations areenough to describe anharmonicity: one to obtain the polymorphous structure andone to obtain the phonon dispersion at a given temperature. Taken all together, ournew theoretical advances [1.2] pave the way for elucidating the fundamentalmechanisms governing the peculiar optoelectronic and transport properties of halideperovskites.[1] M. Zacharias, G. Volonakis, F. Giustino, and J. Even, “Anharmonic electronphononcoupling in polymorphous perovskites” (2022), submitted[2] M. Zacharias, G. Volonakis, F. Giustino, and J. Even, "Anharmonic lattice