The excitonic couplings among 54 bacteriochlorophylls-g (BChl)-g, 4 BChl-g', and 2 Chl-aF pigments were calculated in the type-I homodimeric reaction center (RC) of Heliobacterium modesticaldum (hRC) and compared with those in the photosystem I (PSI) type-I heterodimeric RC. The advanced combination of transition charge of electrostatic potential (TrESP) with the Poisson equation (Poisson-TrESP), applied for the first time to the excitonic coupling calculation, gave a reliable model in contrast to a model calculated by simple standard dipole-dipole interaction approximation that was qualitatively valid for hRC but not for PSI. The simplest method for the calculation of the long-range contribution to the excitonic coupling on RCs is shown to be the TrESP method, which considers a distance- and orientation-independent local-field/screening correction factor. The excitonic couplings of the special pairs, P800 in hRC and P700 in PSI, are also calculated by the fragment excitation difference scheme at the configuration-interaction singles (CIS) level, which considers the charge-transfer characteristics of the relevant excitonic states. The calculation realized that the reported parameter values for P800 and P700 were better than the Poisson-TrESP calculation. Virtual exchanges between Chl-a and BChl-g on hRC and PSI indicated that the difference between hRC and PSI arises from the different electronic structures of Chl-a and BChl-g pigments themselves and the different arrangements on hRC and PSI. The contributions of excitonic couplings to the functional properties and evolutionary modifications of hRC and PSI are also discussed.

中文翻译：

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Heliobacterial对称I型反应中心上的激子耦合：与光系统I的比较。

计算了54个细菌叶绿素-g（BChl）-g，4个BChl-g'和2个Chl-aF颜料之间的激子偶合，并在模式细菌（hRC）的I型同二聚反应中心（RC）中进行了比较。光系统I（PSI）I型异二聚体RC。静电势的过渡电荷（TrESP）与泊松方程（Poisson-TrESP）的高级组合首次应用于激子耦合计算，与简单的标准偶极-偶极相互作用所计算的模型相比，该模型提供了可靠的模型对于hRC在定性上有效，但对PSI无效的近似值。计算RCs上的激子耦合的远距离影响的最简单方法是TrESP方法，它考虑了与距离和方向无关的局部场/屏蔽校正因子。特殊对的激子耦合，hRC中的P800和PSI中的P700，也是通过构型相互作用单（CIS）级别的片段激发差分方案计算的，其中考虑了相关激子态的电荷转移特性。计算结果表明，所报告的P800和P700参数值优于Poisson-TrESP计算。Chl-a和BChl-g在hRC和PSI上的虚拟交换表明，hRC和PSI之间的差异是由Chl-a和BChl-g颜料本身的电子结构不同以及hRC和PSI的不同排列引起的。