For the CHARMM family of force fields we tested, we find that CHARMM22* and CHARMM27 similarly overstabilize the native state, while CHARMM36 predicts a mostly unfolded ensemble. All three CHARMM force fields predict negligible misfolded populations. A unique aspect in all the CHARMM force fields tested is the use of grid-based energy correction map (CMAP) to empirically improve backbone dihedral angle distributions with respect to experiment. 82 CHARMM22* improves upon CHARMM22 by introducing CMAP corrections for glycine and proline residues, and modifying aspartic acid, glutamic acid and arginine amino acids. 12 CHARMM27 saw the complete integration of CMAP corrections into CHARMM22. CHARMM36 is an improvement upon CHARMM22/CMAP with a revisedbackbone CMAP and sidechain torsion potentials optimized against small macromolecules. 7 However, this force field was shown to display a high left-handed αhelix propensity inconsistent with experimental observations, motivating the development of CHARMM36m. Our results corroborate the inaccuracy of CHARMM36, which predicts an unfolded population of 93%, resulting in by far the largest reduced chi-squared value of all force fields we tested. Although we did not test CHARMM36m, some insight into its performance can be gained from Huang et al. who performed simulations of chignolin and its more stable variant CLN025 to validate the performance of CHARMM36m. They found that CHARMM36m predicts only a 2.6% native state population of chignolin, but predicts a 41% native population for CLN025.