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运用点偶极、单极跃迁电荷和跃迁密度等经典库仑作用的方法,考察了叶绿素a分子间面心距和错位结构等因素对激子耦合的影响.结果表明,当分子间距大于分子尺寸时,上述三种方法得到的结果基本一致;但当分子间距小于分子尺寸时,点偶极方法将明显高估激子耦合,跃迁密度的方法更适合计算分子间的激子耦合.此外,还使用上述方法计算了光系统Ⅰ(PSI)反应中心叶绿素a分子间激子耦合.结果表明,用跃迁密度计算PSI晶体结构(1jb0.pdb)P700的激子耦合为75.3cm?1,而QM-MM优化的结构P700(ecA1-ecB1)的激子耦合为23.8cm?1,这与考虑Dexter交换项的全对角化方法的结果(20cm?1)一致,进而说明PSI反应中心并不是传统的P700强激子耦合对,而是ecA1-ecB2和ecB1-ecA2对强耦合二聚体构成的二聚体对.
By using the classical coulomb effect of point dipole, unipolar transition charge and transition density, the influence of the centroid distance and the dislocation structure of chlorophyll a molecules on the exciton coupling is investigated. The results show that when the molecular distance is larger than the molecular size , The results obtained by the above three methods are basically the same; however, when the molecular distance is smaller than the molecular size, the point dipole method will significantly overestimate the exciton coupling, and the transition density method is more suitable for calculating the intermolecular exciton coupling. The above method was used to calculate the exciton coupling between chlorophyll a molecules in PSI reaction center.The results showed that the exciton coupling of P700 with PSI crystal structure (1jb0.pdb) calculated by transition density was 75.3 cm -1, while QM-MM The exciton coupling of the optimized structure P700 (ecA1-ecB1) is 23.8 cm -1, which is consistent with the result of the full diagonalization method (20 cm -1) considering the Dexter exchange term, thus indicating that the PSI reaction center is not a traditional P700 Strong exciton coupling pairs, but rather the dimer pairs of strongly coupled dimers formed by ecA1-ecB2 and ecB1-ecA2.