This problem is equivalent to assessing the wellness of fit between two potential energy surfaces -DFT (reference) and MACE (fitted) in our case. In the first instance, two structures relaxed by the two methods can be compared by computing root mean squared displacement (RMSD) between the atoms' positions. However, there are several options from which to start geometry optimisation with each method, as depicted in As discussed above, this value over-estimates the error, because some of the DFT and MACErelaxed structures correspond to non-equivalent local minima. The most sensibly computed RMSEs correspond to 1.37 and 1.24 kcal/mol, where both DFT and MACE BDEs were computed on DFT and MACE-re-relaxed structures, which ensures that the BDEs are computed and compared on equivalent local minima.