Some methods in the SAMPL7 challenge achieved a good prediction accuracy for pK a 's. Figure shows the performance comparison of methods based on accuracy with RMSE and MAE. Two submissions achieved a RMSE < 1.0 pK a units, no methods achieved a RMSE ≤ 0.5 pK a units. One of the methods that achieved a RMSE < 1.0 pK a units was a QM-based physical prediction method (EC_RISM ), and the other was a QSPR/ML method that was submitted as a reference method (REF00_Chemaxon_Chemicalize ).