Roden Jan J J, Bennett Doran I G, Whaley K Birgitta
Department of Chemistry, University of California, Berkeley, California 94720, USA.
J Chem Phys. 2016 Jun 28;144(24):245101. doi: 10.1063/1.4953243.
We simulate the long-range inter-complex electronic energy transfer in photosystem II-from the antenna complex, via a core complex, to the reaction center-using a non-Markovian (ZOFE) quantum master equation description that allows the electronic coherence involved in the energy transfer to be explicitly included at all length scales. This allows us to identify all locations where coherence is manifested and to further identify the pathways of the energy transfer in the full network of coupled chromophores using a description based on excitation probability currents. We investigate how the energy transfer depends on the initial excitation-localized, coherent initial excitation versus delocalized, incoherent initial excitation-and find that the overall energy transfer is remarkably robust with respect to such strong variations of the initial condition. To explore the importance of vibrationally enhanced transfer and to address the question of optimization in the system parameters, we systematically vary the strength of the coupling between the electronic and the vibrational degrees of freedom. We find that the natural parameters lie in a (broad) region that enables optimal transfer efficiency and that the overall long-range energy transfer on a ns time scale appears to be very robust with respect to variations in the vibronic coupling of up to an order of magnitude. Nevertheless, vibrationally enhanced transfer appears to be crucial to obtain a high transfer efficiency, with the latter falling sharply for couplings outside the optimal range. Comparison of our full quantum simulations to results obtained with a "classical" rate equation based on a modified-Redfield/generalized-Förster description previously used to simulate energy transfer dynamics in the entire photosystem II complex shows good agreement for the overall time scales of excitation energy transport.
我们使用非马尔可夫（ZOFE）量子主方程描述来模拟光系统II中的长程复合物间电子能量转移——从天线复合物，经由核心复合物，到反应中心——该描述允许在所有长度尺度上明确包含能量转移中涉及的电子相干性。这使我们能够识别出相干性表现的所有位置，并使用基于激发概率流的描述进一步识别耦合发色团全网络中的能量转移途径。我们研究了能量转移如何依赖于初始激发——局域化、相干的初始激发与离域化、非相干的初始激发——并发现总体能量转移对于初始条件的这种强烈变化具有显著的稳健性。为了探究振动增强转移的重要性并解决系统参数优化问题，我们系统地改变电子与振动自由度之间的耦合强度。我们发现自然参数处于一个（宽泛的）区域，该区域能够实现最佳转移效率，并且在纳秒时间尺度上的总体长程能量转移对于高达一个数量级的电子 - 振动耦合变化似乎非常稳健。然而，振动增强转移对于获得高转移效率似乎至关重要，对于超出最佳范围的耦合，转移效率会急剧下降。将我们的全量子模拟结果与基于先前用于模拟整个光系统II复合物中能量转移动力学的修正雷德菲尔德/广义福斯特描述的“经典”速率方程所获得的结果进行比较，结果表明在激发能量传输的总体时间尺度上两者吻合良好。
