Preferred oriented cation configurations in high pressure phases IV and V of methylammonium lead iodide perovskite

Abstract

A microscopic viewpoint of structure and dipolar configurations in hybrid organic–inorganic perovskites is crucial to understanding their stability and phase transitions. The necessity of incorporating dispersion interactions in the state-of-the-art density functional theory for the CH3NH3PbI3 perovskite (MAPI) is demonstrated in this work. Some of the vdW methods were selected to evaluate the corresponding energetics properties of the cubic MAPI with various azimuthally rotated MA organic cation orientations. The highest energy barrier obtained from PBEsol reaches 18.6 meV/MA-ion, which is equivalent to 216 K, the temperature above which the MA cations randomly reorient. Energy profiles calculated by vdW incorporated functionals, on the other hand, exhibit various distinct patterns. The well-developed vdW-DF-cx functional was selected, thanks to its competence, to evaluate the total energies of different MA dipolar configurations in 2 × 2 × 2 cubic supercell of MAPI under pressures. The centrosymmetric arrangement of the MA cations that provide zero total dipole moment configuration results in the lowest energy state profiles under pressure, while the non-centrosymmetric scheme displays a unique behaviour. Despite being overall unpolarised, the latter calculated with PBEsol leads to a rigid shift of energy from the profile obtained from the dispersive vdW-DF-cx functional. It is noteworthy that the energy profile responsible for the maximum polarised configuration nevertheless takes the second place in total energy under pressure.