Dynamic DFT calculations using Ab Initio molecular dynamics (MD) were performed with the CP2K package. As was used in VASP, all calculations employed the PBE exchangecorrelation potential along with the GD3/BJ dispersion correction. The Molopt double zeta valence plus polarisation basis sets were used with GTH PBE pseudopotentials. Full details of the protocols used for the NPT and NVT simulations are reported in the SI (Section 4). Some of the static and dynamical calculations employed super-cells a full description of which are given in the SI (Section 6). A super-cell is indicated by the use of the "SC" or "DC" designation followed by the polymorph, followed by the number of molecules in the cell and optionally a letter to distinguish between cells. Thus SCII8 refers to a super-cell of Form II with 8 molecules in the super-cell. Where there is some disorder in hydrogen bonding pattern the designation "DC" is used instead of "SC" and therefore DCI32 would refer to a disordered cell of Form I containing 32 molecules. All calculations using super-cells were performed without symmetry constraints.