Humphries Ben S, Green Dale, Jones Garth A
School of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom.
J Chem Phys. 2022 Feb 28;156(8):084103. doi: 10.1063/5.0077404.
We elucidate the influence of the system-bath boundary placement within an open quantum system, with emphasis on the two-dimensional electronic spectra, through the application of the hierarchical equations of motion formalism for an exciton system. We apply two different models, the Hamiltonian vibration model (HVM) and bath vibration model (BVM), to a monomer and a homodimer. In the HVM, we specifically include the vibronic states in the Hamiltonian capturing vibronic quenching, whereas in the BVM, all vibrational details are contained within the bath and described by an underdamped spectral density. The resultant spectra are analyzed in terms of energetic peak position and thermodynamic broadening precision in order to evaluate the efficacy of the two models. The HVM produces 2D spectra with accurate peak positional information, while the BVM is well suited to modeling dynamic peak broadening. For the monomer, both models produce equivalent spectra in the limit where additional damping associated with the underdamped vibration in the BVM approaches zero. This is supported by analytical results. However, for the homodimer, the BVM spectra are redshifted with respect to the HVM due to an absence of vibronic quenching in the BVM. The computational efficiency of the two models is also discussed in order to inform us of the most appropriate use of each method.
我们通过对激子系统应用运动方程分层形式，阐明了开放量子系统中系统 - 浴边界位置的影响，重点关注二维电子光谱。我们将两种不同的模型，即哈密顿振动模型（HVM）和浴振动模型（BVM），应用于单体和同二聚体。在HVM中，我们在哈密顿量中专门纳入了捕捉电子 - 振动猝灭的电子 - 振动态，而在BVM中，所有振动细节都包含在浴中，并由欠阻尼谱密度描述。根据能量峰位置和热力学展宽精度对所得光谱进行分析，以评估这两种模型的有效性。HVM产生具有准确峰位置信息的二维光谱，而BVM非常适合对动态峰展宽进行建模。对于单体，在BVM中与欠阻尼振动相关的额外阻尼接近零的极限情况下，两种模型产生等效光谱。这得到了解析结果的支持。然而，对于同二聚体，由于BVM中不存在电子 - 振动猝灭，BVM光谱相对于HVM发生红移。还讨论了这两种模型的计算效率，以便为我们提供每种方法最合适的使用方式。
