Fig. 1: Phonons and phase transitions in CsPbBr3. | Communications Physics

Fig. 1: Phonons and phase transitions in CsPbBr3.

From: Limits of the phonon quasi-particle picture at the cubic-to-tetragonal phase transition in halide perovskites

Fig. 1

a Phonon dispersion for the cubic phases of CsPbBr3 obtained using the machine-learned potential (MLP) in the harmonic approximation, 0 K (dashed lines) and from an effective harmonic model (EHM) at 500 K (solid lines). b Potential energy landscape along the unstable M-tilt mode calculated with MLP and density functional theory (DFT). The inset shows the CsPbBr3 crystal structure (Cs purple, Pb gray, Br red) in the energy minima, for which the PbBr6 octahedra have been tilted in-phase (visualization made with OVITO75). c–e Lattice parameters and mode coordinates obtained from a cooling run based on the isothermal–isobaric (NpT) ensemble with phase transitions at approximately 300 K and 275 K. In c–e Solid, dashed, and dotted lines refer to the Cartesian directions x, y, and z, respectively.

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