To evaluate the performance of ML models trained on XALKENEDB with out-of-training samples, we conducted quantum chemical reference calculations on a 2D-potential energy surface comprising 3731 points (41×91 points). This grid was constructed based on the most stable equilibrium geometry of ethene, propene, and butene, respectively. We scanned the distance of the alkene C=C bond between 2.000 and 3.000 Bohr in 41 steps of 0.025 Bohr, and varied the HC=CH dihedral angle from 0 to 180 • in 2 • increments (91 steps). For each geometry, electronic properties were obtained at the SA(3)-CASSCF(2,2)/cc-pVDZ level of theory for the three lowest-lying singlet states, as detailed above (iii). The corresponding data is available in the XALKENEDB, identified by the string 'grid' within the subset name.