Many physical phenomena must be accounted for to accurately model solution-phase optical spectral line shapes, from the sampling of chromophore-solvent configurations to the electronic-vibrational transitions leading to vibronic fine structure. Here we thoroughly explore the role of nuclear quantum effects, direct and indirect solvent effects, and vibronic effects in the computation of the optical spectrum of the aqueously solvated anionic chromophores of green fluorescent protein and photoactive yellow protein. By analyzing the chromophore and solvent configurations, the distributions of vertical excitation energies, the absorption spectra computed within the ensemble approach, and the absorption spectra computed within the ensemble plus zero-temperature Franck-Condon approach, we show how solvent, nuclear quantum effects, and vibronic transitions alter the optical absorption spectra. We find that including nuclear quantum effects in the sampling of chromophore-solvent configurations using ab initio path integral molecular dynamics simulations leads to improved spectral shapes through three mechanisms. The three mechanisms that lead to line shape broadening and a better description of the high-energy tail are softening of heavy atom bonds in the chromophore that couple to the optically bright state, widening the distribution of vertical excitation energies from more diverse solvation environments, and redistributing spectral weight from the 0-0 vibronic transition to higher energy vibronic transitions when computing the Franck-Condon spectrum in a frozen solvent pocket. The absorption spectra computed using the combined ensemble plus zero-temperature Franck-Condon approach yield significant improvements in spectral shape and width compared to the spectra computed with the ensemble approach. Using the combined approach with configurations sampled from path integral molecular dynamics trajectories presents a significant step forward in accurately modeling the absorption spectra of aqueously solvated chromophores.

中文翻译：

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利用核量子效应揭示电子吸收光谱：水中的光敏黄色蛋白和绿色荧光蛋白发色团

从生色团-溶剂构型的采样到导致振动精细结构的电子振动跃迁，必须考虑许多物理现象才能精确地模拟溶液相光谱线的形状。在这里，我们彻底探索核量子效应，直接和间接溶剂效应以及振动效应在绿色荧光蛋白和光敏黄色蛋白的水溶剂化阴离子发色团的光谱计算中的作用。通过分析生色团和溶剂构型，垂直激发能的分布，在集成方法中计算的吸收光谱以及在集成加零温度的Franck-Condon方法中计算的吸收光谱，我们展示了溶剂，核量子效应，和电子跃迁改变了光吸收光谱。我们发现，使用发色团-溶剂构型的采样将核量子效应包括在内从头开始路径积分分子动力学模拟通过三种机制改善了光谱形状。导致线形变宽和对高能尾部进行更好描述的三个机制是发色团中重原子键的软化，该重原子键耦合到光学亮态，拓宽了来自更多不同溶剂化环境的垂直激发能的分布，并且计算冻结溶剂袋中的弗兰克-康登光谱时，将光谱权重从0-0振动转变为高能振动转变。与使用集成方法计算的光谱相比，使用组合集成方法加上零温度的Franck-Condon方法计算的吸收光谱在光谱形状和宽度方面产生了显着改善。