where θ c is the central angle, usually 90 • ; θ l and θ u are lower and upper limits, being 45 • and 135 • by default. Hence the range of random perturbations is shifted towards 90 • and then scaled by the cut-off. The non-uniform sampling of unit cell angle perturbations means that the simulation does not fulfill detailed balance, which is unimportant here because the BH approach focuses on prediction of local minima on the energy landscape, rather than a distribution at equilibrium. Since molecular perturbations were applied to the asymmetric unit, the cutoff on volume change depended on the number of molecules in the primitive unit cell to eliminate the impact from different space groups with different numbers of symmetry operations.