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.
