With the primary goal of improving pK a prediction performance we probed the pK a values of wild type DsbA and seven mutants. Because changes in ϵ had a limited effect on solvent structure or solvation free energy, we decided to only scan σ-values on the interval [0.8, 1.5]. We observed a sigmoidal improvement in accuracy that was saturated for σ = 1.3 with an AUE of 2.88 ± 0.24 pK (Figure ) and a Pearson correlation of 0.31 ± 0.60. This accuracy was significantly increased from unscaled Amber14SB which had an AUE of 5.21 ± 0.44 pK and a correlation of 0.00 ± 0.51 on the DsbA test set.