Of the five important TTBI structures (the four observed polymorphs and the global energy minimum, which we label ε), four (all but α) have space group symmetries that could be sampled in either space group P 1 or P 2 1 /c with one independent molecule (Z = 1). The results of threshold simulations performed in P 1 and P 2 1 /c, starting trajectories from β, γ, δ and ε, are shown in Figure and. All searches used 5 kJ mol -1 increments in the lid energy and 1,000 steps were attempted at each lid energy.