Absorption and Circular Dichroism Spectra of Molecular Aggregates With the Full Cumulant Expansion.
Absorption and Circular Dichroism Spectra of Molecular Aggregates With the Full Cumulant Expansion.
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DOI：
10.1021/acs.jpcb.0c05180
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发表时间：
2020-10-01
期刊：
影响因子：
--
通讯作者：
Cao J
中科院分区：
文献类型：
--
作者：
Cupellini L;Lipparini F;Cao J
多色聚集体的激子哈密顿量可以用线性吸收和圆二色性等光谱技术来探测。为了将计算的哈密顿量与实验进行比较，需要考虑激子与分子间和分子内振动耦合的线形理论。这种耦合通常通过累积展开形式以微扰方式引入，并通过假设马尔可夫激子动力学进一步近似，例如使用修正的Redfield理论。在这里，我们提出了全累积展开（FCE）形式的实现（,,），以有效地计算吸收和圆二色光谱的分子聚集体超越马尔可夫近似，不受激子-声子耦合形式的限制。以紫色细菌的LH2体系为例，我们将FCE线形与修正Redfield理论得到的马尔可夫线形进行了比较，发现后者与实验结果的一致性较差。相反，FCE方法准确地描述了线形，特别是在B800峰的振动边带。我们设想FCE方法将成为精确比较模型激子哈密顿量与光学光谱实验的有价值的工具。
The exciton Hamiltonian of multichromophoric aggregates can be probed by spectroscopic techniques such as linear absorption and circular dichroism. To compare calculated Hamiltonians to experiments, a lineshape theory is needed, which takes into account the coupling of the excitons with inter- and intramolecular vibrations. This coupling is normally introduced in a perturbative way through the cumulant expansion formalism and further approximated by assuming a Markovian exciton dynamics, for example with the modified Redfield theory. Here, we present the implementation of the full cumulant expansion (FCE) formalism (, , ) to efficiently compute absorption and circular dichroism spectra of molecular aggregates beyond the Markov approximation, without restrictions on the form of exciton–phonon coupling. By employing the LH2 system of purple bacteria as a challenging test case, we compare the FCE lineshapes with the Markovian lineshapes obtained with the modified Redfield theory, showing that the latter presents a less satisfying agreement with experiments. The FCE approach instead accurately describes the lineshapes, especially in the vibronic sideband of the B800 peak. We envision that the FCE approach will become a valuable tool for accurately comparing model exciton Hamiltonians with optical spectroscopy experiments.
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