In contrast, deviation from Rabi oscillation behavior is observed for TDHF propagation. The maximum LUMO population is 0.31, 0.58, and 0.76 for System 1, for fields with strengths of 0.001, 0.003, and 0.005 a.u. applied for 100, 60, and 20 fs, respectively. Systems 2 and 3 have closer to full population of the LUMO, with maximum occupation values of 0.84 and 0.99 for field-strength of 0.003 a.u. However, all systems also show an additional high frequency oscillation of the population when the LUMO is maximally occupied, indicative of a mixed state rather than being purely in the S 1 state, and System 3 also no longer undergoes full population inversion after three Rabi cycles, which is presumably due to occupation of higher lying states as we see increased occupation of the virtual space, see discussion below.