As expected, the calculated physical properties of the two polymorphs (Table ) show only marginal differences. The total lattice energy of form II is calculated to be 0.293 kJ mol -1 higher than form I, which implies that form I is marginally the more energetically stable state. The energy difference increases to 1.609 kJ mol -1 when considering also the zero-point energies. The cohesive energy (Ecohesive per molecule) of form I is predicted to be 0.560 kJ mol -1 lower than form II prior to any correction for BSSE, but rises to 0.035 kJ mol -1 higher than form II after BSSE correction. A noticeable difference is that the entropy of form I is predicted to be smaller than that of form II. It should be noted that this refers to vibrational entropy, calculated for the idealised form I and form II crystal structures. The calculations do not quantify configurational entropy associated with the structural disorder described for form II single crystals.