The threshold simulations in P 1 and P 2 1 /c yield disconnectivity graphs with similar structures and high energy barriers between the initial structures (lid energies at which transitions are found are summarised in Table ). The connectivity structure shows a deep energy basin centered on ε with very few higher energy connected local minima until the energy lid is increased to very high energies. In the P 1 simulation, β, δ and ε are all connected at the same lid energy, +155 kJ mol -1 above ε (+110 kJ mol -1 above δ and 67 kJ mol -1 above β). The results are very similar in P 2 1 /c. As with the indigo polymorphs, there is a slight lowering of the lid energies at which several of the transitions occur in this larger unit cell: the connection between β and δ is lowered by 10 kJ mol -1 compared to the P 1 results, while their connection to ε is lowered by only 5 kJ mol -1 .