用变分Monte Carlo和多体格林函数理论计算姜黄素阴离子型的S1 <- S0理论吸收能
Theoretical S1 <- S0 absorption energies of the anionic forms of oxyluciferin by Variational Monte Carlo and Many Body Green's Function Theory
摘要：
萤火虫荧光素（OxyLuc）的三种负电荷形式（阴离子酮-1和烯醇-1，双阴离子烯醇-2）的结构在变分蒙特卡罗（VMC）水平上得到了完全弛豫.用TDDFT、CC 2和多体格林函数理论（MBGFT）计算了S_1 <-S_0垂直跃迁的吸收能。通过Bethe-Salpeter（BS）形式主义，在VMC结构上使用MBGFT提供了与通过酮-1形式（2.32 eV）的作用光谱实验获得的值（2.26（8）eV）非常一致的结果。为了解开的作用，优化的基态几何形状的质量，BS激发能也已计算CASSCF几何形状，诱导一个不可忽略的蓝移（0.08和0.07 eV的酮-1和烯醇-1形式，分别）相对于VMC的。结构效应已被分析的过度或不足的相关性沿共轭键的OxyLuc通过使用不同的方法的基态优化。酮-1和烯醇-1形式的S $_1$态的相对稳定性取决于选择用于激发态计算的方法，因此代表对这些系统的任何理论研究的基本警告。最后，Kohn-Sham HOMO和LUMO轨道的烯醇-2（几乎）绑定只有当二价阴离子被嵌入到溶剂（水和甲苯在本工作中）;激发态计算因此是有意义的，只有在存在的介电介质中的本地化的电子密度。结合VMC的基态几何和BS形式的吸收光谱明显优于标准的TDDFT和量子化学方法。
英文摘要：
The structures of three negatively charged forms (anionic keto-1 and enol-1, dianonic enol-2) of oxyluciferin (OxyLuc), which are the most probable emitters responsible for the firefly bioluminescence, have been fully relaxed at the variational Monte Carlo (VMC) level. Absorption energies of the S1<-S0 vertical transition have been computed using different levels of theory, such as TDDFT, CC2 and many body Green's function Theory (MBGFT). The use of MBGFT, by means of the Bethe-Salpeter (BS) formalism, on VMC structures provides results in excellent agreement with the value (2.26(8) eV) obtained by action spectroscopy experiments for the keto-1 form (2.32 eV). To unravel the role of the quality of the optimized ground state geometry, BS excitation energies have also been computed on CASSCF geometries, inducing a non negligible blue shift (0.08 and 0.07 eV for keto-1 and enol-1 forms, respectively) with respect to the VMC ones. Structural effects have been analyzed in terms of over- or under-correlation along the conjugated bonds of OxyLuc by using different methods for the ground-state optimization. The relative stability of the S$_1$ state for the keto-1 and enol-1 forms depends on the method chosen for the excited state calculation, thus representing a fundamental caveat for any theoretical study on these systems. Finally, Kohn-Sham HOMO and LUMO orbitals of enol-2 are (nearly) bound only when the dianion is embedded into a solvent (water and toluene in the present work); excited state calculations are therefore meaningful only in presence of a dielectric medium which localizes the electronic density. The combination of VMC for the ground state geometry and BS formalism for the absorption spectra clearly outperforms standard TDDFT and quantum chemistry approaches.
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