than WTMetaD-IB AL (192), with WTMetaD-IB AL exhibiting a more uniform sampling (Fig. ). The quality of the resulting MLPs was evaluated using an independent test set from a 3 ps US/AIMD simulation at the PBE0-D3BJ/def2-SVP level of theory, with a reaction coordinate of r 1 -r 2 , where r 1 corresponds to the C-C distance between the shifted methyl group and its original position and r 2 is the C-C distance between the same methyl group and its new position (upper part in Fig. ). This simulation provided 326 testing data points, collected every 10 fs. On this test set, WTMetaD-IB AL performs slightly better than downhill AL, with energy and force errors of 1.49 meV atom -1 and 161.76 meV Å -1 , respectively, which are 0.27 meV atom -1 and 13.34 meV Å -1 lower than those obtained using downhill AL (Table ). The MLP trained with WTMetaD-IB AL shows the highest errors around the TS region, defined as -0.2 Å < r 1 -r 2 < 0.0 Å, with the DFT TS located at r 1 -r 2 ≈ -0.1 Å (Fig. ). In this region, MAE in energy and force are 4.27 meV atom -1 and 290.24 meV Å -1 , respectively.