In the last years, several methods and parameters have been tested on fulvene, which represents the perfect playground also to test the PESs at different CASPT2 flavors. Indeed, no dynamics have been run along different CASPT2 surfaces and extensively compared. We first ran AIMS/SA-2-CASSCF(6,6)/6-31G* dynamics on a group of 18 initial conditions (IC) offered to the community to test their method on. All the electronic structure calculations used an active space of 6 electrons and 6 orbitals, corresponding to the π system of the molecule and the corresponding π* orbitals, and include two singlet electronic states. The full list of parameters for the dynamics is reported in the Supporting Information. These ICs differ for the initial geometry and they all have a zero momentum associated. The dynamics are shown in Figure3, and it is compared with the same level of theory, but with the difference of the electronic structure software (OpenMolcas vs. MOLPRO) and the implementation of the AIMS algorithm (PySpawn vs FMS90). The CASSCF relaxation profile of S 1 is analogous in the two simulations, although a slightly different amount of the reflected population ( 11 vs 16%), which can be attributed to the different implementations of the AIMS algorithm, in particular, the way the time-derivative coupling (TDC) is computed, 57 the spawning threshold is defined, the use of an adaptive time step and the momentum rescaled after a spawn. The difference in population between the two nonadiabatic dynamics codes and electronic structure codes is not surprising as very small differences in gradients or couplings can have a large impact on the nonadiabatic dynamics. We also note that the number of initial conditions, 18, is somewhat limited despite the faster convergence of AIMS simulations in comparison with conventional independent trajectory approaches. As each initial condition creates a branch of multiple interacting TBFs, over longer times the simulations are expected to converge well as at the end of the propagation the number has grown to a total of 125 TBFs.