The effects of the lattice modulation on the intermolecular motions of the MA cations of the tetragonal MAPbI3 phase

Abstract Quite recently, it was shown both experimentally and theoretically that the electronic properties of MAPbI 3 in the tetragonal phase can be affected by both MA + cations and distortions of PbI 3 + and phonons play an important role in the dynamical electronic properties. In particular, the fluctuation of MAPbI 3 due to phase transition is also important. In this work, we shed light on the nature of the phonons in the THz region by constructing a model system, performing the first‐principles simulation method, and analyzing the normal mode via the energy decomposition method. Our simulations show that, near the phase transition condition with a particular MA1 and MA2 orientational configuration, the hydrogen atoms of MA2 will participate in the phonon in the THz region with framework distortion of PbI 3 + .