The good fitting result relies on appropriate training data. The training trajectories naturally sample the important parts of the conformational space including the areas of high hopping probabilities. Fig. shows a close view of the crucial area, i.e. where the S 1 and S 2 surfaces are close to each other, which is explored by the trajectory after about 48 fs. The fitted PE surfaces (dashed) show a slightly larger energy gap than the model PE surfaces (solid).