Instead we sampled the cell dipole every 0.5 ps and calculated the dielectric permittivity of the cell from the dipole moment correlation function. Full details of the method used is provided in the SI (Section 5) and the scripts used to perform the calculation are available. This approach is subject to more noise than the methods used within the Travis package, but should capture the correlations between molecules that Travis does not consider, which may be important for THz spectral prediction. In the SI we compare the results obtained for the absorption spectrum using both methods and this shows reasonable agreement between them for frequencies above 400 cm -1 but larger spectral differences below. The Travis program was used to analyse the molecular dynamics trajectories to determine the dihedral angle distribution functions.