Brillouin zone boundary acoustic phonon modes of methylammonium lead iodide Perovskite (MAPI)

These animations show the Brillouin zone boundary acoustic phonon modes of methylammonium lead iodide perovskite (MAPI). The underlying phonon eigenmode calculations use the PBE GGA functional to relax the structure and calculate the forces.<br>In these animations, the iodine and lead atoms are coloured purple and green, respectively. The methylammonium cation (CH3NH3) is drawn with carbon as red, nitrogen as blue and hydrogen as white.<br>The material is in the pseudo-cubic structure, which we take to be representative of the room-temperature structure.<br>The pseudo-cubic unit cell is expanded into a 4x4x4 supercell, and the zone boundary (pi/a) modes shown, with neighbouring unit cells being out of phase in their motion. The motion is made by modulating the atomic positions with the phonon eigenvectors according to a sinusoidal function to produce harmonic motion.<br>The size of the displacements were arbitrarily set to make the atomic motion clear, and are not representative of the actual amplitude.<br>For calculation details, see: http://dx.doi.org/10.1103/PhysRevB.92.144308.<br>This work was developed for the following paper, where zone-boundary phonon modes were studied experimentally:http://dx.doi.org/10.1021/acsenergylett.6b00381<br><br>The supercell animations were generated by the ascii-phonons package in conjunction with the Blender ray-tracing software, using phonon eigenvectors from Phonopy.<br>See here for the underlying Phonopy data files containing the dynamic matrix:https://github.com/WMD-group/Phonons/tree/master/2015_MAPbI3