采用多级实时光子嵌入方法研究卤化物核心光谱的溶剂化效应
Solvation effects on halides core spectra with Multilevel Real-Time quantum embedding
AI总结：
本研究提出结合BOMME与FDE的新型多级实时光子嵌入方法，通过水溶液卤离子XAS计算验证，该方法能平衡精度与成本，为溶剂化体系光谱模拟提供新途径。
摘要：
本研究提出了一种新型的基于子系统的电子结构嵌入方法，该方法将基于投影的块正交化Manby-Miller嵌入（BOMME）与基于密度的冻结密度嵌入（FDE）方法相结合。对于构成单元间存在不同强度相互作用的体系，该方法十分有效，且相较于对整个体系进行量子模拟，其计算成本更低。\n为评估方法性能，我们通过实时含时密度泛函理论（rt-TDDFT）计算，测试了该方法重现水溶液中氯离子和氟离子X射线吸收光谱（XAS）的能力（基于50个水分子的液滴模型）。我们采用系综方法计算K边和L边的XAS，使用了通过可极化力场经典分子动力学模拟得到的多个构型空间快照。构型平均会影响光谱特征的展宽及其强度，最终强度的贡献来自不同的几何构型。\n研究发现，对于卤化物-水的特异性相互作用过于近似的嵌入模型（如FDE），无法重现氯离子的实验光谱。而BOMME由于有限尺寸效应，往往会高估强度，尤其是高能特征峰的强度。将第二溶剂化壳层采用FDE、第一溶剂化壳层保留BOMME的组合方案可缓解这一效应，使实验光谱能量范围内的整体一致性得到提升。此外，我们计算了相关跃迁的跃迁密度，证实这些跃迁发生在卤化物体系内。因此，我们的实时QM/QM/QM嵌入方法被证明是模拟溶剂化体系XAS的一种很有前景的方法。
英文摘要：
In this work we introduce a novel subsystem-based electronic structure embedding method that combines the projection-based block-orthogonalized Manby-Miller embedding (BOMME) with the density-based Frozen Density Embedding (FDE) methods. Our approach is effective for systems in which the building blocks interact at varying strengths while still maintaining a lower computational cost compared to a quantum simulation of the entire system. To evaluate the performance of our method, we assess its ability to reproduce the X-ray absorption spectra (XAS) of chloride and fluoride anions in aqueous solutions (based on a 50-water droplet model) via real-time time-dependent density functional theory (rt-TDDFT) calculations. We employ an ensemble approach to compute XAS for the K- and L-edges, utilizing multiple snapshots of configuration space obtained from classical molecular dynamics simulations with a polarizable force field. Configurational averaging influences both the broadening of spectral features and their intensities, with contributions to the final intensities originating from different geometry configurations. We found that embedding models that are too approximate for halide-water specific interactions, as in the case of FDE, fail to reproduce the experimental spectrum for chloride. Meanwhile, BOMME tends to overestimate intensities, particularly for higher energy features because of finite-size effects. Combining FDE for the second solvation shell and retaining BOMME for the first solvation shell mitigates this effect, resulting in an overall improved agreement within the energy range of the experimental spectrum. Additionally, we compute the transition densities of the relevant transitions, confirming that these transitions occur within the halide systems. Thus, our real-time QM/QM/QM embedding method proves to be a promising approach for modeling XAS of solvated systems.
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