For a two-level system, increasing the intensity of the applied resonant field increases the frequency of population oscillation. With the three systems propagated with the TDCIS method, we indeed see the population driven at a faster rate between S 0 and S 1 , with little population of other states. To directly compare TDCIS and TDHF maximum populations, we next scan the time for which the external resonant sinusoidal field is turned on as well as scan the field strength. The range of field-strengths is between 0.005 and 0.075 a.u., and the number of fieldcycles is between 1 and 10. In Fig. the map of maximum virtual MO occupations during the resonant field application is shown for a range of field strengths and number of field cycles. The TDCIS method produces nearly uniform maximum occupation of one electron as long as the field is on long enough and is intense enough. However, this behavior does not hold for the TDHF electron density propagation, where we instead see much different maximum virtual populations and much higher populations of the virtual orbital space. For all three systems, we see that a more intense field leads to higher occupation of the virtual space, well beyond the single electron occupation of the LUMO. With the field parameters explored, System 1 approaches nearly double occupation of the LUMO, System 2 has three electrons in the virtual MOs, and System 3 has five to six electrons in the virtual space for the more intense fields. The greater population of System 3 could be expected, given that there are many more excited states that could be occupied for a larger system. Overall, this population map suggests that for TDHF electron propagation, applying a field resonant with the S 0 → S 1 transition populates states much higher lying than the S 1 state, and that the resonant field does not lead to well-behaved population oscillation between S 0 and S 1 .