The molecular dynamics simulations of super-cell DCI32 at 88 K, 300 K and 350 K were used to calculate the absorption spectrum of the dispersed disorder in Form I. The results from simulations at the two higher temperatures leads to very similar absorption profiles (Figures and). In the frequency regime between 100 and 400 cm -1 the low temperature spectrum has sharper absorptions which are shifted to higher wavenumber, consistent with a lattice vibration in a smaller volume. The predicted low frequency spectrum (Figure ) is calculated from the cell dipole moment using a window function to give narrower peaks and greater resolution than that used for the frequencies above 400 cm Equally good agreement between the calculated and experimental spectra is also seen when the calculations include such hydrogen bonding, which indicates that this region of the spectrum does not discriminate well between the hydrogen bond motifs seen at high temperature in Form I. The intense peak above 1500 cm -1 is due to deformation of the ammonium ion while the 4 peaks below 1500 cm -1 are mainly methylene group deformations. Close comparison of both calculated spectra and experiment shows an improved correlation between experiment and the dynamic rather than the static calculation. This is largely because in the dynamic calculation no assumption has been made about harmonicity or spectral peak shape which leads to a general shift to lower frequencies compared to the static calculation, particularly for modes below 500 cm -1 . The increased integrated absorption observed for dynamic calculations at lower frequencies also seems to correlate well with the relative absorption seen in the experiment, particularly for the two larger peaks below 300 cm -1 . As has been mentioned previously, the terahertz region should be more sensitive to the type of intermolecular bonding found in the crystal. Experimental results are available in this region from the work of Korter et al. and Ren et al. Here we compare our calculations with spectra digitised from the publications of Ren et al. Figure compares the calculated spectra of Form I with and without disorder from MD at 88 K and static DFT calculations of the SH...S bonding pattern with the experimental spectrum at 83 K. Above 50 cm -1 the static calculation predicts four weak absorption peaks of similar intensity, which in the MD calculations have overlapped into a single broad peak with significantly higher integrated intensity. The window used for the dipole correlation function in this case was chosen to produce narrower peak widths. MD of the SCI8 structure without disorder predicts broad absorption peaks at 100 cm -1 and 122 cm -1 which correlate well with experiment. While the peak at 122 cm -1 is present in the static calculation, peaks around 100 cm -1 shows significantly more structure and less broadening than is seen experimentally or in the dynamic calculation of the non-disordered calculation.