Comparison of Linear Response Theory, Projected Initial Maximum Overlap Method, and Molecular Dynamics-Based Vibronic Spectra: The Case of Methylene Blue
Comparison of Linear Response Theory, Projected Initial Maximum Overlap Method, and Molecular Dynamics-Based Vibronic Spectra: The Case of Methylene Blue
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线性响应理论、投影初始最大重叠法和基于分子动力学的振动光谱的比较：以亚甲基蓝为例
DOI：
10.1021/acs.jctc.1c01127
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发表时间：
2022
影响因子：
5.5
通讯作者：
Isborn, Christine M.
中科院分区：
文献类型：
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作者：
Abou Taka, Ali;Lu, Shao-Yu;Gowland, Duncan;Zuehlsdorff, Tim J.;Corzo, Hector H.;Pribram-Jones, Aurora;Shi, Liang;Hratchian, Hrant P.;Isborn, Christine M.
光学光谱的模拟对于分子表征是必不可少的，在许多情况下，对于解释实验光谱也是至关重要的。模拟振动吸收光谱最常用的方法是对基态和激发态的简正模进行几何优化和计算。在这份报告中，我们指出，在绝热线性响应(LR)理论框架内使用这种方法可能会导致态混合和Born-Oppenheimer近似的崩溃，从而导致对吸收光谱的描述不佳。相比之下，通过自洽场方法结合最大重叠模型计算激发态产生的状态不受这种混合的影响。我们表明，后一种方法产生的振动光谱与垂直梯度和基于分子动力学(MD)轨迹的方法更一致。对于亚甲基蓝发色团，我们比较了以下几种方法计算的振动吸收光谱：具有LR理论优化结构和简正模的绝热Hessian方法，垂直梯度程序，最大重叠法优化结构的Hessian和简正模式，以及由MD轨迹产生的激发能时间关联函数。由于明亮的S1表面和暗的S2表面在S1极小值附近混合，用LR理论计算绝热Hessian，用B3LYP密度泛函计算含时密度泛函理论，预测了吸收光谱的大振动肩，这在任何其他方法中都不存在。我们分析了光谱密度，并比较了在LR理论中强耦合到光激发的关键简正模的行为，同时显示了S1/S2态的混合。总体而言，我们的研究提供了使用LR理论优化结构的激发态绝热Hessian计算振动谱时的注意事项，并展示了三种对绝热混合效应不太敏感的替代方案。
The simulation of optical spectra is essential to molecular characterization and, in many cases, critical for interpreting experimental spectra. The most common method for simulating vibronic absorption spectra relies on the geometry optimization and computation of normal modes for ground and excited electronic states. In this report, we show that the utilization of such a procedure within an adiabatic linear response (LR) theory framework may lead to state mixings and a breakdown of the Born–Oppenheimer approximation, resulting in a poor description of absorption spectra. In contrast, computing excited states via a self-consistent field method in conjunction with a maximum overlap model produces states that are not subject to such mixings. We show that this latter method produces vibronic spectra much more aligned with vertical gradient and molecular dynamics (MD) trajectory-based approaches. For the methylene blue chromophore, we compare vibronic absorption spectra computed with the following: an adiabatic Hessian approach with LR theory-optimized structures and normal modes, a vertical gradient procedure, the Hessian and normal modes of maximum overlap method-optimized structures, and excitation energy time-correlation functions generated from an MD trajectory. Because of mixing between the bright S1and dark S2surfaces near the S1minimum, computing the adiabatic Hessian with LR theory and time-dependent density functional theory with the B3LYP density functional predicts a large vibronic shoulder for the absorption spectrum that is not present for any of the other methods. Spectral densities are analyzed and we compare the behavior of the key normal mode that in LR theory strongly couples to the optical excitation while showing S1/S2state mixings. Overall, our study provides a note of caution in computing vibronic spectra using the excited-state adiabatic Hessian of LR theory-optimized structures and also showcases three alternatives that are less sensitive to adiabatic state mixing effects.