As a final test, we tested whether the poor energy ranking of the ATZ crystal structure is a limitation of the GGA functional used in DFT re-optimization of structures. 11 CSP structures, including the global energy minimum, of ATZ were selected from the DFT reoptimized set, evenly sampling the low energy range. Single-point PBE0 calculations were performed with the GD3BJ dispersion correction to assess the extent of re-ranking by changing to a hybrid DFT functional. The reranking was found to be up to a few kJ mol -1 (see Figure ), which lowered the relative energy of the match to the experimental structure to 5.65 kJ mol -1 (among this subset of structures). PBE0 energy calculations did not significantly affect the relative energies of structures with the 2H-tautomer compared to the 1H tautomer. These results hint that the outlier results for ATZ could be due to limitations of GGA functionals, which are known to suffer from self-interaction error. However, it is plausible that the reported experimental crystal structure of ATZ is in fact a meta-stable polymorph and the true thermodynamically stable polymorph is present within our predicted landscape.