Unlike indigo, the polymorphs of this co-crystal differ in their hydrogen bonding (Fig. ): polymorph I has nicotinamide doubly hydrogen bonded dimers connected by hydrogen bonds to benzoic acid molecules, while polymorph II contains an extended hydrogen-bonded nicotinamide chain with benzoic acid hydrogen bonding to the nicotinamide pyridyl nitrogen atoms at the edges of these chains. Threshold simulations were started from the structures from the CSP landscape (Fig. ) corresponding to I and II. I and II have very similar calculated lattice energies (I has a calculated lattice energy 0.6 kJ mol -1 below II) and are located in the low energy region of the landscape. Due to the greater complexity of the landscape, 3,000 steps were performed at each value of the lid energy, which was increased in 5.0 kJ mol -1 steps up to 150.0 kJ mol -1 above the initial structures, i.e. 30 increases in the threshold energy and a total of 90,000 attempted perturbations from each starting structure.