Terahertz spectroscopy is an ideal method to investigate the effect of the different intermolecular interactions occurring in this system as it probes the lattice vibrations of the crystal. However, calculations of the absorptions at these low frequencies are known to be difficult to perform and sensitive to the details of the calculation. In this paper we report theoretical calculations using both static and molecular dynamic DFT calculations to examine the nature of the hydrogen bonding in all the polymorphs of l-cysteine in an effort to shed further light on the nature of the disorder which occurs in this material.