Herein, we selected butene (C 4 H 8 ) in both cisand transconfigurations, along with the methylenimmonium cation (CH 2 NH + 2 ) as our model systems. For predicting absorption spectra we trained a SpaiNN model on energies (E j ), forces (F j ), NACs (C ij ), and dipole moment vectors (µ µ µ ij ), utilizing both SchNet and PaiNN representations. The absorption spectra obtained from quantum chemical reference calculations and SpaiNN predictions are displayed in Figures 2 and Figures and. Notably, including F j and C ij in the training is crucial for subsequent simulations of geometries at conical intersections and photodynamics (see section 4.3 and 4.4). For butene, we con- ducted reference calculations using SA(3)-CASSCF(2,2)/cc-pVDZ for 451 cisand trans-configurations. These configurations were generated by sampling geometries with varied HC = CH dihedral angles and C = C bond lengths. Specifically, for the cis-configuration, we scanned 11 equidistant dihedral angles between 0 to 20 • and 41 equidistant alkene bond lengths between 2.0 and 3.0 Bohr. Similarly, for the trans-configuration, the same C = C alkene bond lengths were scanned with dihedrals ranging from 160 to 180 • . The corresponding absorption spectra are depicted in Figure as solid, unfilled curves. Additionally, we utilized a SpaiNN model trained on 13 k Wigner sampled structures of butene (cf. ESI section S2.1) for predicting E j and µ µ µ ij of these 902 geometries. Figure illustrates that the ML predicted spectra closely resemble the reference calculations (see filled vs. the times for the whole training and per epoch indicated by the number of epochs in parenthesis as well as the prediction times obtained by averaging the prediction of 1,000 structures 100 times. In none of the training procedures the number of maximum epochs (100 k) was reached and the training was stopped earlier when the validation loss was not changing over 300 epochs. Training was performed on a Tesla-P100 GPU (16 GB RAM) using an Intel Xeon Gold 6134 CPU @ 3.20GHz. Predictions were performed on an Intel(R) Core(TM) i5-12500. unfilled curves), capturing key spectral features and trends between the cisand trans-configurations of butene. Specifically, the maxima of the cisand trans-absorption bands align, while the absorption band of the cis-configurations appears spectrally broader (by 0.14 eV full-width-half-height) compared to the trans-configurations (reference: 0.08 eV difference in full-width-half-height). Figure depicts the SpaiNN predicted absorption bands (filled curves) of CH 2 NH + 2 for nπ * (S 0 -to-S 1 , dark green) and ππ * photoexcitation (S 0 -to-S 2 , bright green). The corresponding absorption spectrum obtained for the same 20,000 structures via MR-CISD(6,4)/aug-cc-pVDZ is presented as a solid green line in Figure , as previously reported by some of us. It is evident that the SpaiNN model of CH 2 NH + 2 , accurately predicts absorption bands that closely resemble the reference absorption spectrum.