For the reaction R2, the US/MLP-MD free energy profile was computed using r 1 -r 2 as the reaction coordinate, split into 30 equally-spaced windows with a force constant of 20 eV Å -2 . The simulation ran for 40 ps at 365.6 K in every window and the first 10 ps in each window were used for equilibration and discarded from the analysis. Free energy was calculated by the weighted histogram analysis method (WHAM) as implemented in mlp-train. WTMetaD was performed along the same reaction coordinate, r 1 -r 2 , as the US.