In subsequent iterations, both approaches successfully sample the PES, as shown in the right panel of Fig. The accuracy of the MLIPs was evaluated by comparing the predicted energies with those obtained from the ground-truth method (CPCM(water)-PBE0-D3BJ/def2-SVP) along the intrinsic reaction coordinate (IRC, Fig. ) obtained from DFT calculations. The mean absolute error (MAE) in the energy for the trained MLIPs is 2.66 meV atom -1 for downhill AL and 2.12 meV atom -1 for WTMetaD-IB AL. Both values are within chemical accuracy (1 kcal, equating to 43 meV and 7.16 meV atom -1 for this system). The predicted energy errors for each configuration in the IRC are depicted in the subplot of Fig. . The individual predicted energies for both MLIPs are below 1 kcal mol -1 as well, except for one data point predicted by MLIP trained using the downhill AL with an error of 7.16 meV atom -1 (1 kcal mol -1 ). Interestingly, while the TS optimised by the ground-truth method was not provided in WTMetaD-IB AL, the MLIP trained using this method still reached a higher accuracy for the TS with an error of 2.37 meV atom We evaluated the quality of the trained MLIPs using an independent test set obtained from a 3.2 ps umbrella sampling (US) simulation at the ground-truth level of theory (US/AIMD).