论文标题
Decalized电子激发及其在Rhodobacter Sphaeroides反应中心的定向电荷转移中的作用
Delocalized Electronic Excitations and their Role in Directional Charge Transfer in the Reaction Center of Rhodobacter Sphaeroides
论文作者
论文摘要
在紫色细菌中,驱动辐射能向化学能转化为化学能的基本电荷分离步骤沿着一个分支 - A分支 - 杂二聚体色素 - 蛋白质复合物(反应中心)。在这里,我们将第一原理与时间依赖性密度功能理论(TDDFT)和最佳调整范围分离的杂交功能一起研究\ textIt {rhodobacter sphaeroides}的反应中心的主要六种颜料的电子和激发态结构。通过在我们的TDDFT计算中明确包含围绕这六种颜料的氨基酸残基,我们会系统地研究蛋白质环境对能量和电荷转移激发的影响。我们的计算表明,与第一个电荷转移到B分支的能量转移明显低于向B分支,与单向电荷转移一致。我们进一步表明,将蛋白质环境的加入重新缩短了这种激发,从而可以从耦合$ q_x $激发的能量转移。通过分析过渡和差异密度,我们证明了大多数$ q $ band激励在几种颜料上都强烈取代,并且它们的空间离域化和电荷转移特征都决定了它们受热激活的分子振动的强大影响。我们的结果提出了一种在这个细菌反应中心中电荷转移的机制,并为进一步的第一原告研究了对离域激发态,振动耦合以及该和其他复杂的轻度收获系统蛋白质环境的作用的相互作用的第一原理研究。
In purple bacteria, the fundamental charge-separation step that drives the conversion of radiation energy into chemical energy proceeds along one branch - the A branch - of a heterodimeric pigment-protein complex, the reaction center. Here, we use first principles time-dependent density functional theory (TDDFT) with an optimally-tuned range-separated hybrid functional to investigate the electronic and excited-state structure of the primary six pigments in the reaction center of \textit{Rhodobacter sphaeroides}. By explicitly including amino-acid residues surrounding these six pigments in our TDDFT calculations, we systematically study the effect of the protein environment on energy and charge-transfer excitations. Our calculations show that a forward charge transfer into the A branch is significantly lower in energy than the first charge transfer into the B branch, in agreement with the unidirectional charge transfer observed experimentally. We further show that inclusion of the protein environment redshifts this excitation significantly, allowing for energy transfer from the coupled $Q_x$ excitations. Through analysis of transition and difference densities, we demonstrate that most of the $Q$-band excitations are strongly delocalized over several pigments and that both their spatial delocalization and charge-transfer character determine how strongly affected they are by thermally-activated molecular vibrations. Our results suggest a mechanism for charge-transfer in this bacterial reaction center and pave the way for further first-principles investigations of the interplay between delocalized excited states, vibronic coupling, and the role of the protein environment of this and other complex light-harvesting systems.