Habenicht Bradley F, Tani Noriyuki P, Provorse Makenzie R, Isborn Christine M
Chemistry and Chemical Biology, University of California Merced, Merced, California 95343, USA.
J Chem Phys. 2014 Nov 14;141(18):184112. doi: 10.1063/1.4900514.
We investigate the Rabi oscillations of electrons excited by an applied electric field in several simple molecular systems using time-dependent configuration interaction (TDCI) and real-time time-dependent density-functional theory (RT-TDDFT) dynamics. While the TDCI simulations exhibit the expected single-electron Rabi oscillations at a single resonant electric field frequency, Rabi oscillations in the RT-TDDFT simulations are a two-electron process. The existence of two-electron Rabi oscillations is determined both by full population inversion between field-free molecular orbitals and the behavior of the instantaneous dipole moment during the simulations. Furthermore, the Rabi oscillations in RT-TDDFT are subject to an intensity threshold of the electric field, below which Rabi oscillations do not occur and above which the two-electron Rabi oscillations occur at a broad range of frequencies. It is also shown that at field intensities near the threshold intensity, the field frequency predicted to induce Rabi oscillations by linear response TDDFT only produces detuned Rabi oscillations. Instead, the field frequency that yields the full two-electron population inversion and Rabi oscillation behavior is shown to be the average of single-electron transition frequencies from the ground S0 state and the doubly-excited S2 state. The behavior of the two-electron Rabi oscillations is rationalized via two possible models. The first model is a multi-photon process that results from the electric field interacting with the three level system such that three level Rabi oscillations may occur. The second model suggests that the mean-field nature of RT-TDDFT induces paired electron propagation.
我们使用含时组态相互作用（TDCI）和实时含时密度泛函理论（RT - TDDFT）动力学方法，研究了在几个简单分子系统中由外加电场激发的电子的拉比振荡。虽然TDCI模拟在单个共振电场频率下展现出预期的单电子拉比振荡，但RT - TDDFT模拟中的拉比振荡是一个双电子过程。双电子拉比振荡的存在既由无场分子轨道之间的完全布居反转决定，也由模拟过程中瞬时偶极矩的行为决定。此外，RT - TDDFT中的拉比振荡受到电场强度阈值的限制，低于该阈值拉比振荡不会发生，高于该阈值双电子拉比振荡会在很宽的频率范围内出现。研究还表明，在接近阈值强度的场强下，线性响应TDDFT预测会诱发拉比振荡的场频率只会产生失谐的拉比振荡。相反，能产生完全双电子布居反转和拉比振荡行为的场频率被证明是基态S0和双激发态S2的单电子跃迁频率的平均值。双电子拉比振荡的行为通过两种可能的模型得到了合理的解释。第一个模型是一个多光子过程，它源于电场与三能级系统相互作用，从而可能发生三能级拉比振荡。第二个模型表明，RT - TDDFT的平均场性质会诱发成对电子的传播。
