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Two Distinct Modes of Hydrogen-Bonding Interaction in the Prototypic Hybrid Halide Perovskite, Tetragonal CH3NH3PbI3

In spite of the key role of hydrogen bonding in the structural stabilization of the prototypic hybrid halide perovskite, CH3NH3PbI3 (MAPbI3), little progress has been made in our in-depth understanding of the hydrogen-bonding interaction between the MA+-ion and the iodide ions in the PbI6-octahedron network. Herein, we show that there exist two distinct types of the hydrogen-bonding interaction, naming a- and b-modes, in the tetragonal MAPbI3 on the basis of symmetry argument and density-functional theory calculations. The computed Kohn-Sham (K-S) energy difference between these two interaction modes is 45.14 meV per MA-site with the a-interaction mode being responsible for the stable hydrogen-bonding network. We have further estimated the individual bonding strength for the ten relevant hydrogen bonds having a bond critical point. The net difference in the total hydrogen-bonding energies between these two interaction modes is 43.87 meV per MA-site, which nearly coincides with the K-S energy difference of 45.14 meV.