To examine the differences between the electron dynamics calculated using TDCIS and RT-TDHF methods for the three systems of interest in the presence of a resonant field, we apply a sinusoidal driving field for the entire duration of propagation with a field-frequency equal to the S 0 → S 1 transition energy at maximum field strengths of 0.001, 0.003, and 0.005 a.u. The molecules are not formally two-level systems, so some deviation from ideal Rabi oscillation behavior is expected. As the populations of electronic states cannot be directly quantified with TDHF, we use the occupation of the virtual orbital space as a quantifier of the deviation of TDHF electron dynamics from ideal behavior. Because the S 0 → S 1 transition is primarily HOMO → LUMO in character, we monitor the occupation of the LUMO as a metric for population of the S 1 state. See Fig. for population oscillation with an applied field of E max = 0.003 a.u. Plots with E max = 0.001 and 0.005 a.u. are shown in SI Figures and. The TDCIS behavior is as expected, with population oscillating between the S 0 and S 1 states as seen by near single occupation of the LUMO for each system; the maximum population of the LUMO is 0.95, 0.95 and 0.94 e for Systems 1, 2, and 3, respectively. The maximum value remains consistent throughout the duration of the applied field, over many Rabi cycles. Additionally, the frequency of the population oscillation is well within the numerical error (O(10 -5 a.u.)) of the expected Rabi frequency for all three systems.