However, in this IC, the various flavors of CASPT2 actually play a role. The main features of the overall dynamics are in common: slower first spawn with respect to CASSCF, a certain amount of population transferred to the ground state, part of it later reflected to the first singlet state, and finally no further decay to S 0 in the first 40fs. However, slightly different profiles can be noticed. First, although less drastic, the spawn of the first child is slightly scattered from 10.9 to 12.0 fs. More interestingly, both the amount of population decayed to the ground state and the reflected one, vary in the four CASPT2 dynamics, due to the distinct surfaces and couplings between TBFs. XMS-CASPT2 and XDW-CASPT2 show a very limited amount of population decayed to the ground state (around 30%) followed by a small degree of reflection. Much more population is initially transferred at MS-CASPT2 level (ca. 70%), while a full relaxation is observed in the RMS-CASPT2 dynamics. These last two show a comparable S 1 relaxation after reflection. Another important difference worth it to be underlined is the different way the population is transferred back to S 1 . While for CASSCF the child spawns back when it encounters again the CoIn after a few fs, this happens even faster in the even more sloped CoIn in CASPT2 the overlap between the two TBFs is high enough to prevent a second child from being spawned, but not to the population to be transferred back to S 1 due to the strong coupling between the two Gaussians. The overall behavior can be better understood by looking again at relative energies and TDC between the two singlet states (Figure6c,d). At CASPT2 levels the two surfaces cross only once, when the CASSCF ones had already crossed twice. It is important to stress that RMS-CASPT2 and XMS-CASPT2 are the only two flavors that show a perfectly conserved total energy of the parent TBF in IC15 (Figure5B), while MS-CASPT2 and XDW-CASPT2, with a not drastic but still interesting jump, show some degree of discontinuity once are they passing through the CoIn. On the contrary, along IC8 the total energy is perfectly smooth at any CASPT2 level, as the deactivation channel through the peaked CoIn is and indeed the parent TBF does not encounter it and does not manifest any discontinuity in the total energy (Figure5A).