The trained GB parameters also provide a large improvement in accuracy for the hostguest test set, which, with 90 systems, is about three times the size of the training set (Figure and Table ). Just as for the training set, the binding free energies are overestimated with the original mBondi2 radii, especially for the cucurbit[n]uril complexes, and the new radii correct this bias. Going from the original radii to the trained set reduces the overall RMSE from 19.5 to 2.1 kcal/mol and the R 2 value from 0.5 to 0.8. The cucurbit[n]uril complexes improved the most, with RMSE falling from 32.1 to 2.8 kcal/mol. Similarly, cyclodextrin complexes improved from 3.4 to 1.2 kcal/mol, while the RMSE stayed roughly the same for octa-acids. We see a big improvement in the R 2 value for cucurbit[n]urils and octa-acids, but the value fell slightly from 0.6 to 0.5 for cyclodextrins. and.