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.
Temperature Evolution of Methylammonium Trihalide Vibrations at the Atomic Scale / Mattoni, A; Filippetti, A.; Saba, M. I.; Caddeo, C.; Delugas, Pietro Davide. - In: THE JOURNAL OF PHYSICAL CHEMISTRY LETTERS. - ISSN 1948-7185. - 7:3(2016), pp. 529-535. [10.1021/acs.jpclett.5b02546]
Temperature Evolution of Methylammonium Trihalide Vibrations at the Atomic Scale
DELUGAS, Pietro Davide
2016-01-01
Abstract
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.File | Dimensione | Formato | |
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