Full CSP data tables for these box plots can be found in the supplementary information. Figure shows an example CSP result for 2-methyl-5-nitramino-2H-tetrazole (MNT), where a predicted structure matching the experimentally determined structure is identified as the second lowest energy structure (Figure ) and the structure reproduces the experimentally determined crystal structure accurately (RMSD 30 = 0.190 Å, Figure ). To evaluate the force fields, we examined how well they reproduced the experimentally determined crystal structures by measuring the RMSD 30 between the experimental structure and its match within each CSP set, and the relative energy of the match to the experimental structure. The best performing force field and electrostatic model combination is that which minimizes the RMSD 30 , which measures structural deviations between predicted and experimental crystal structures, and ranks the matches to the observed crystal structures well (low energies relative to the global energy minimum). No choice of force field emerges from this study as performing better than the others by both measures. The best force field at ranking energies of the observed crystal structures (W99rev + B3LYP/6-31G**(PCM)) produces the largest geometric deviations, whereas that producing the smallest range of RMSD 30 (W99rev + B3LYP/6-31G**) gives the worst overall performance on energy ranking. Without a clear optimum from these results, we proceed with the FIT force field, which produces a small range in RMSD 30 and low median relative energies in these tests, and performs best in previous benchmarks against measured sublimation enthalpies for a variety of small organic crystal systems.