On the one hand, in recent work on the photo-isomerization dynamics of trans-azobenzene using CTTSH (see Section IV B), it was necessary to freeze some high-energy internal vibrations while performing the initial harmonic Wigner sampling to avoid creating highly energetic trajectories: due to the limited number of affordable CTTSH trajectories (100 and 150 coupled trajectories were used) in such a large nuclear configuration space (of 72 dimensions), the energetic trajectories were rapidly separating in space and needed to be decoupled from the rest of the ensemble for numerical convenience, essentially reducing CTTSH to standard surface hopping. With a similar idea in mind, in order to avoid ensembles, or bundles, of trajectories that dramatically diverge in configuration space, the independent bundle approximation (IBA) was proposed using CTMQC . The IBA consists in organizing N tr trajectories in n bundles each containing n tr trajectories, such that N tr = n × n tr , where the n tr trajectories are grouped in the bundles according to their initial kinetic energy (or potential energy, or total energy, etc.). On the other hand, the initialization of the electronic dynamics in a pure adiabatic state is the commonly-accepted practice for photochemical studies, since with a femtosecond laser pulse it is possible to target the excitation of a low-lying electronic state. Nonetheless, photo-ionization with an attosecond laser pulse, broadly distributed in energy, is capable of creating a coherent superposition of electronic states (see Section IV C). For applications in attochemistry, then, the way of creating such a superposition should be adapted to the used simulation method as well as to the observables under investigation, as discussed in Ref. [142].