To this end, GPR surrogates for the twisted-pyramidalized MECI of ethylene were constructed using MR-CIS single point energies. To compare the ω and c z 0 GPR surrogates computed using MR-CIS and DFT/MRCI(2) energies, we consider the resulting learned kernel hyperparameters. These values are given in Table . The difference in the tilt parameters can then be directly related to the learned hyperparameters. It can be seen that apart from the noise term, the learned variance σ 2 and lengthscale l of c z 0 (R) is similar between DFT/MRCI(2) and MR-CIS. The straight-forward interpretation of these results is that the two learned surfaces are similar in terms of how large and how rapidly the c z 0 (R) surface is varying around a MECI, which are reflected in the lengthscale and variance, respectively. The DFT/MRCI(2)-based surrogates have a larger noise term to account for the local energetic variations. The two ω(R) surfaces, however, are different, with the DFT/MRCI(2)-based surrogate having appreciably smaller σ 2 and l hyperparameters. Examining Eq. 14 and taking the gradient of ω(R), we can see that the tilt parameters are proportional to σ 2 and inversely proportional to l,