N lower values for the other 15 observed crystal structures are shown in Fig. for the four energy models -FIT+DMA and the three dimer-corrected models -with ∆E comparisons given in Fig. . It should first be noted that the majority of molecules studied here were selected on the basis that they are known to be challenging for force field methods. This is reflected in the large N lower values for many of the structures at the force field (FIT+DMA) level: