From our CSP calculations, candidate structures matching well with published structures for forms I, II and IV (RMSD26 of 0.04, 0.13 and 0.20 Å in reference to CSD structures UNOGIN03, UNOGIN04 and UNOGIN05) are sampled and ranked among the top 5 of the candidate list (Figure ). In agreement with the previous study, we find that forms I and IV are highly competitive in energy with an energy difference of only around 0.1 kcal/mol as obtained from using both the r 2 SCAN-D3 and the PBE0-MBD methods. In addition, the lattice parameters of one of the low-lying predicted structures in the Pbca space group (Rank 3) has very similar lattice parameters and structure (RMSD28 of 0.32 Å) as compared to form III* . The simulated PXRD data of our best match Pbca structure show many of the characteristic peaks which were assigned to form III (see Figure in SI). These comparisons indicate that the rank 3 predicted structure in the Pbca space group might be a putative structure of form III (Following the nomenclature in Ref. , we refer our best match Pbca structure as form III * in Figure ).