Indigo and tetrolic acid are both small, hydrogen bonding molecules, each with two known polymorphs. Both indigo polymorphs have the same space group symmetry and the same network of hydrogen bonds. In contrast, the polymorphs of tetrolic acid occupy different space groups and differ in hydrogen bonding. We also study the co-crystal formed between nicotinamide and benzoic acid, which is referred by the Cambridge Structural Database reference code of its known crystal structure , GAZCES. The cocrystal system has both experimental structures in the same space group, P 2 1 /c, but with changes in the arrangement of hydrogen bonds. Triptycene trisbenzimidazolone (TTBI), has a more complex energy landscape and four experimen-tally observed polymorphs distributed over a wide energy range.