The temperature evolution of vibrations of CH3NH3PbI3 (MAPI) is studied by combining first principles and classical molecular dynamics and compared to available experimental data. The work has a fundamental character showing that it is possible to reproduce the key features of the vibrational spectrum by the simple physical quantities included in the classical model, namely the ionic-dispersive hybrid interactions and the mass difference between organic and inorganic components. The dynamics reveals a sizable temperature evolution of the MAPI spectrum along with the orthorhombic-to-tetragonal-to-cubic transformation and a strong dependence on molecular confinement and order. The thermally induced weakening of the H-I interactions and the anharmonic mixing of modes give two vibrational peaks at 200-250 cm-1 that are not present at zero temperature and are expected to have detectable infrared activity. The infrared inactive vibrational peak at ?140 cm-1 due to molecular spinning disappears abruptly at the orthorhombic-to-tetragonal transition and forms a broad molecular band red-shifting progressively with temperature. This trend is correlated to the reduced confinement of the rotating cations due to thermal expansion of the lattice. © 2016 American Chemical Society.
|Titolo:||Temperature Evolution of Methylammonium Trihalide Vibrations at the Atomic Scale|
|Autori:||Mattoni, A; Filippetti, A.; Saba, M.I.; Caddeo, C.; Delugas, P.|
|Data di pubblicazione:||2016|
|Digital Object Identifier (DOI):||10.1021/acs.jpclett.5b02546|
|Appare nelle tipologie:||1.1 Journal article|