The calculation revealed that the double features near 1.7 THz originate from three distinct lattice vibrational motions predicted to be at 1.74 THz, 1.93 THz and 1.96 THz. As outlined above, the slight overestimation of the vibrational frequencies is attributable to the simulation being performed at 0 K while the experimental data is acquired at temperatures ≥ 80 K. produced by ss-DFT. The reason behind this absence is not clear. The use of other basis sets and density functionals did not produce the lower feature, nor did the explicit calculation of transverse optical (TO) and longitudinal optical (LO) phonon splitting. One possible explanation is that the published space group of P 2 1 2 1 2 1 is not an accurate representation of the symmetry of the crystal at reduced temperatures and is instead P 2 1 as suggested by others. A reduction in crystal symmetry may yield new vibrations in the ss-DFT predicted spectra, but such simulations are not trivial given the high computational cost of the much larger asymmetric unit.