In the top panel of Fig. , the populations of the dia-batic state 2 are shown. To determine this population, we apply the transformation matrix from the adiabatic to the diabatic basis, which is available via QuantumMod-elLib, to the coefficients of the BH-like of the electronic state. For the TSH-based methods, we only calculate the diabatic population if P S2 (t) F S2 (t). In the same panel, we report MCTDH results from Ref. [ 73] as reference, but the comparison with the trajectory-based methods shows that the two sets of dynamics, i.e., quantum and quantum-classical, are not initialized in the same way, which is related to the fact that the CI between S 1 and S 2 is close to the FC region. Nonetheless, in general, the diabatic population of state 2 reflects a similar behavior as in the adiabatic picture, with only a different behavior at short times, with a decay to less than 10% during the first 10 fs. We will show below at the end of this section a similar analysis of the diabatic population using the same initial conditions as in MCTDH.