The pair of polymorphs related by the lowest energy barrier is α and β, where the lid energy at which their trajectories meet is just under 50 kJ mol -1 above the calculated energy of α. The result agrees with molecular dynamics studies in which the structures of all other observed TTBI polymorphs showed only fluctuations about their known crystal structures at 300K, apart from α, which partially transformed to β in a short, 500 ps, simulation. These structures also occupy the same 'spike' on the energydensity representation of the crystal structure landscape. We note that the disconnectivity graph tends to group structures of similar density; the lowest energy barriers tend to be found between structures that are close in density.