Intermolecular Coulomb couplings from ab initio electrostatic potentials: Application to optical transitions of strongly coupled pigments in photosynthetic antennae and reaction centers
Intermolecular Coulomb couplings from ab initio electrostatic potentials: Application to optical transitions of strongly coupled pigments in photosynthetic antennae and reaction centers
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DOI：
10.1021/jp0615398
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发表时间：
2006-08-31
影响因子：
3.3
通讯作者：
Renger, T.
中科院分区：
文献类型：
--
作者：
Madjet, M. E.;Abdurahman, A.;Renger, T.
本文提出了一种计算分子间电子状态电荷密度和电子激发跃迁密度之间库仑耦合的精确而有效的方法。跃迁密度的耦合产生Forster类型的激发能量转移耦合，而电荷密度耦合导致分子激发能的移动。从电荷密度和跃迁密度的从头算出发，确定原子的部分电荷，以便与不同状态和跃迁产生的静电势相匹配。然后，通过原子部分电荷之间的库仑耦合得到不同的分子间耦合。将本方法得到的激发能转移耦合与简单的点-偶极近似、扩展偶极近似以及Kruger、Scholes和Fleming的从头算跃迁密度立方方法的计算结果进行了比较。本方法具有与后者相同的精度，但计算效率更高。应用该方法研究了绿硫细菌(FMO)、紫细菌(LH2)和高等植物(LHC-II)捕光复合体中的强耦合色素，以及细菌反应中心和光系统I和II的反应中心的“特殊对”。对于天线中的色素二聚体，发现色素的相互取向优化以获得最大的激子耦合。这种取向的驱动力是基态电荷密度之间的库仑耦合。在“特殊对”中激子耦合的情况下，发现所有三个反应中心的点-偶极近似都崩溃了，但如果跃迁偶极的范围被选择得比先前假设的大，扩展的偶极近似工作得令人惊讶地好。对于“特殊对”，由于电荷密度耦合，局域跃迁能发生较大的漂移。
An accurate and numerically efficient method for the calculation of intermolecular Coulomb couplings between charge densities of electronic states and between transition densities of electronic excitations is presented. The coupling of transition densities yields the Forster type excitation energy transfer coupling, and from the charge density coupling, a shift in molecular excitation energies results. Starting from an ab initio calculation of the charge and transition densities, atomic partial charges are determined such as to fit the resulting electrostatic potentials of the different states and the transition. The different intermolecular couplings are then obtained from the Coulomb couplings between the respective atomic partial charges. The excitation energy transfer couplings obtained in the present TrEsp (transition charge from electrostatic potential) method are compared with couplings obtained from the simple point-dipole and extended dipole approximations and with those from the ab initio transition density cube method of Kruger, Scholes, and Fleming. The present method is of the same accuracy as the latter but computationally more efficient. The method is applied to study strongly coupled pigments in the light-harvesting complexes of green sulfur bacteria (FMO), purple bacteria (LH2), and higher plants (LHC-II) and the "special pairs" of bacterial reaction centers and reaction centers of photosystems I and II. For the pigment dimers in the antennae, it is found that the mutual orientation of the pigments is optimized for maximum excitonic coupling. A driving force for this orientation is the Coulomb coupling between ground-state charge densities. In the case of excitonic couplings in the "special pairs", a breakdown of the point-dipole approximation is found for all three reaction centers, but the extended dipole approximation works surprisingly well, if the extent of the transition dipole is chosen larger than assumed previously. For the "special pairs", a large shift in local transition energies is found due to charge density coupling.