Beauchamp et al. used a reduced χ 2 metric to comprehensively rank force fields in comparison with NMR observables for short peptides and ubiquitin. They found AMBER99SBnmr1ildn ? and AMBER99SB-ildn-phi 31 to be the most accurate when coupled with TIP3P solvent. ? Of the force fields they tested, six are force fields we tested for chignolin (AMBER99SBnmr1ildn, AMBER99SB-ildn, OPLS-aa, AMBER99, AMBER99SB, CHARMM27). A comparison of the reduced chi-squared values in each study reveals a similar ranking, with the values strongly correlated (R 2 =0.89, Figure ). Pantelopulos G. et al. simulated MDM2 in complex using 9 different force fields, and similarly used the NMR predictor SHIFTX2 to compare computed and experimental chemical shifts. While many of the force fields performed similarly, only AMBER99SBnmr1-ildn was able to capture helical structuring in the N-terminal lid region.