The polarizable embedding (PE) method is a fully self‐consistent fragment‐based QM/MM approach that uses advanced polarizable force fields and can be applied for various environments, including solvents and DNA. However, lack of proper electronic description of the MM environment can result in electron density leakage from the QM to the MM region, an effect known as electron spill‐out (ESO). ESO can be avoided by applying effective core potentials (ECPs) on MM atoms in PE (PE‐ECP) or by including repulsion operators to model the orthogonality between the two regions, as in the polarizable density embedding (PDE) approach. In this study, the one‐ and two‐photon absorptions of 4′‐(hydroxymethyl)‐4,5′,8‐trimethylpsoralen in complex with DNA and in aqueous solution are investigated. The effect of the missing non‐electrostatic repulsion of the MM region on result accuracy is showcased. While ESO errors are not readily visible for one‐photon absorption spectra, they become significant when computing two‐photon absorption, as more than one excited state is considered. Including ECPs on environment atoms sufficiently addresses the ESO problem, yielding correct structure for excited states. Comparisons with the more advanced PDE model show that PE‐ECP leads to qualitatively correct one‐ and two‐photon absorption spectra.

中文翻译：

---

与DNA配合物对4'-（羟甲基）-4,5'，8-三甲基补骨脂素的单光子和双光子激发建模：解决极化QM / MM计算中的电子溢出问题

可极化嵌入（PE）方法是一种完全自洽的基于片段的QM / MM方法，它使用先进的可极化力场，可应用于包括溶剂和DNA在内的各种环境。但是，缺乏对MM环境的正确电子描述会导致电子密度从QM泄漏到MM区域，这种现象称为电子溢出（ESO）。可以通过在PE（PE-ECP）中的MM原子上施加有效的核心电势（ECP）或通过包括排斥算子来模拟两个区域之间的正交性来避免ESO，如可极化密度嵌入（PDE）方法中那样。在这项研究中，研究了4'-（羟甲基）-4,5'，8-三甲基补骨脂素在与DNA络合物和水溶液中的一光子吸收和二光子吸收。展示了MM区域缺少的非静电排斥力对结果精度的影响。尽管对于单光子吸收光谱来说，ESO误差不容易看到，但在计算两光子吸收率时，ESO误差变得非常重要，因为考虑了多个激发态。包括环境原子上的ECP足以解决ESO问题，从而产生激发态的正确结构。与更高级的PDE模型的比较表明，PE‐ECP可以定性地校正一光子和二光子的吸收光谱。产生激发态的正确结构。与更高级的PDE模型的比较表明，PE‐ECP可以定性地校正一光子和二光子的吸收光谱。产生激发态的正确结构。与更高级的PDE模型的比较表明，PE‐ECP可以定性地校正一光子和二光子的吸收光谱。