Multireference Excitation Energies for Bacteriochlorophylls A within Light Harvesting System 2
Multireference Excitation Energies for Bacteriochlorophylls A within Light Harvesting System 2
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DOI：
10.1021/acs.jctc.5b01104
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发表时间：
2016-03-01
影响因子：
5.5
通讯作者：
De Vico, Luca
中科院分区：
文献类型：
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作者：
Anda, Andre;Hansen, Thorsten;De Vico, Luca
紫色细菌的光捕获系统2（LH 2）是最受欢迎的天线复合体之一，用于研究自然界收集和引导太阳能的方式。吸收能量的动力学是由超快光谱探测。这些实验的模拟依赖于拟合一系列参数来再现光谱。在这里，我们提出了一种方法，可以确定化学精度的关键参数。这将消除建模中的自由变量，从而减少问题。使用MS-RASPT 2/RASSCF计算，我们计算的激发能和跃迁偶极矩的所有细菌叶绿素在LH 2。我们发现，激发能各不相同的细菌叶绿素单体，它们是由大环的曲率和二面角的乙酰基部分。增加曲率提升基态能量，这导致激发能的红移。增加乙酰基部分的扭转提高了激发态能量，导致激发能的蓝移。所获得的结果标志着生物系统光化学中多构型多参考量子化学方法的巨大飞跃，这可以证明有助于揭示光合光捕获的潜在物理学。
Light-harvesting system 2 (LH2) of purple bacteria is one of the most popular antenna complexes used to study Nature's way of collecting and channeling solar energy. The dynamics of the absorbed energy is probed by ultrafast spectroscopy. Simulation of these experiments relies on fitting a range of parameters to reproduce the spectra. Here, we present a method that can determine key parameters to chemical accuracy. These will eliminate free variables in the modeling, thus reducing the problem. Using MS-RASPT2/RASSCF calculations, we compute excitation energies and transition dipole moments of all bacteriochlorophylls in LH2. We find that the excitation energies vary among the bacteriochlorophyll monomers and that they are regulated by the curvature of the macrocycle ring and the dihedral angle of an acetyl moiety. Increasing the curvature lifts the ground state energy, which causes a red shift of the excitation energy. Increasing the torsion of the acetyl moiety raises the excited state energy, resulting in a blue shift of the excitation energy. The obtained results mark a giant leap for multiconfigurational multireference quantum chemical methods in the photochemistry of biological systems, which can prove instrumental in exposing the underlying physics of photosynthetic light-harvesting.