In the remainder of this section, we show results obtained using the TDQT method, where the classical force is obtained as (minus) the gradient of the numerical TDPES. In addition to benchmarking the performance of TDQT against quantum wavepacket propagations, we also compare TDQT against a time-dependent classical trajectory (TDCT) approach, using only the classical force in the integration procedure. For each calculation, 5000 TDCT classical trajectories have been propagated using the same initial condition parameters used for the exact vibronic calculations, sampling the positions and momenta according to the Wigner distribution. Concerning the TDQT simulations, 400 trajectories were used in all cases presented in this section, with an ODE error tolerance of 10 -9 . As quantum trajectory propagation is performed using an adaptive time step method, it was necessary to access the TDPES and associated forces at arbitrary times. A time interpolation procedure was therefore introduced, assuming linear evolution of the TDPES between two adjacent Chebychev time steps. Similarly, a linear spatial interpolation was performed to obtain the TDPES-derived force at arbitrary positions between grid points.