The MCTDH simulations with a sufficient number of SPFs (𝑛 ≥ 12) effectively show a monoexponential decay process with the excited-state lifetime ranging from 7 to 8 ps and the remaining population between 2 to 5% at 50 ps. There are some indications of back population transfer to the excited states after 25 ps for simulations with 𝑛 = 20 and 𝑛 = 24. Nevertheless, at this point, it is unclear whether it is due to any physical processes or numerical instabilities. Interestingly, ML-MCTDH simulations predict a different decay behavior, yielding a bi-exponential nonadiabatic process as depicted by the simulations with 𝑛 ≥ 12. In general, 70% of the excited state population decays within 8 ps, whereas the remaining ones decay around 30 ps.