To what degree these stacks are facing the same direction (i.e. the co-directionality) of the stacks can then be measured by comparison of the average direction of the stacks, and crystal structures with no stacks, or where the maximum stack size was less than 4 were considered 'unstacked'. For all of the stacking analysis, all molecules whose centroids were within 35 Å of the asymmetric unit centroid were considered. The code for this analysis is available upon request.