From the set of initial conditions chosen for FSSH, we run 44 individual CSS-AIMS simulations for the SBH model for 60 ps with the timesteps of 20 and 1 au (0.48 and 0.024 fs) outside and within coupling regions, respectively. However, CSS-AIMS propagates the dynamics predominantly within the coupling region and only uses the larger timestep for the interval in which the initial TBF approaches that region. This behavior contrasts with the earlier implementation of the continuous spawning algorithm, where only one timestep was used, and the simulations started with at least two TBFs. The widths of the frozen Gaussian TBFs are set according to the frequencies of the different vibrational modes as 𝛼 𝑘 = 𝑀 𝑘 𝜔 𝑘 2ℏ