We next discuss results of the aFSSH simulations of PSB3 starting from photoexcitation initial conditions, in which internal coordinates and velocities are sampled from a ground-state Wigner distribution and initiated on the S 1 state at t = 0. Figure shows the timedependent populations of the S 0 and S 1 states averaged over 200 trajectories at each of the three levels of TDDFT that were introduced above. The S 1 population exhibits a delayed exponential decay, meaning that the system remains in the S 1 state for a certain amount of time before the population begins to decrease exponentially. The lifetime of the S 1 state can be obtained by fitting the population p(t) using the function