In the following sections we will explore how the different static and dynamic models described previously can be used for calculating the infrared and terahertz spectra and how these methods influence the resulting calculated spectral properties. As each polymorph has a unique crystal packing structure we focus our discussion on the low frequency infrared response (below 150 cm -1 , which is dominated by external modes of motion) and on the high frequency response associated with the S-H stretching vibration as these are the regions most sensitive to polymorphism, dynamics and disorder although calculated spectra for all spectral regions are available in the SI.