Laboratory of Theoretical Chemistry, Institute of Chemistry, ELTE Eötvös Loránd University, P.O. Box 32, H-1117 Budapest, Hungary.
György Hevesy Doctoral School, Institute of Chemistry, ELTE Eötvös Loránd University, H-1117 Budapest, Hungary.
J Chem Theory Comput. 2023 Jun 27;19(12):3580-3600. doi: 10.1021/acs.jctc.3c00104. Epub 2023 May 26.
While Coupled-Cluster methods have been proven to provide an accurate description of excited electronic states, the scaling of the computational costs with the system size limits the degree for which these methods can be applied. In this work different aspects of fragment-based approaches are studied on noncovalently bound molecular complexes with interacting chromophores of the fragments, such as π-stacked nucleobases. The interaction of the fragments is considered at two distinct steps. First, the states localized on the fragments are described in the presence of the other fragment(s); for this we test two approaches. One method is founded on QM/MM principles, only including the electrostatic interaction between the fragments in the electronic structure calculation with Pauli repulsion and dispersion effects added separately. The other model, a Projection-based Embedding (PbE) using the Huzinaga equation, includes both electrostatic and Pauli repulsion and only needs to be augmented by dispersion interactions. In both schemes the extended Effective Fragment Potential (EFP2) method of Gordon et al. was found to provide an adequate correction for the missing terms. In the second step, the interaction of the localized chromophores is modeled for a proper description of the excitonic coupling. Here the inclusion of purely electrostatic contributions appears to be sufficient: it is found that the Coulomb part of the coupling provides accurate splitting of the energies of interacting chromophores that are separated by more than 4 Å.
虽然耦合簇方法已被证明可提供对激发电子态的准确描述，但随着系统规模的计算成本的扩展限制了这些方法的应用程度。在这项工作中，研究了基于片段的方法的不同方面，这些方法应用于非共价键合的分子复合物，其中包含片段之间相互作用的发色团，例如π-堆积碱基。片段之间的相互作用在两个不同的步骤中进行考虑。首先，在存在其他片段的情况下描述局域在片段上的状态；为此，我们测试了两种方法。一种方法基于 QM/MM 原理，仅在电子结构计算中包括片段之间的静电相互作用，而单独添加 Pauli 排斥和色散效应。另一种模型是使用 Huzinaga 方程的基于投影的嵌入 (PbE)，包括静电和 Pauli 排斥，仅需要增加色散相互作用。在这两种方案中，发现 Gordon 等人的扩展有效片段势 (EFP2) 方法为缺少的项提供了足够的校正。在第二步中，为了对激子耦合进行适当的描述，对局域发色团之间的相互作用进行建模。这里包含纯静电贡献似乎就足够了：发现相互作用的发色团之间的能量分裂，对于彼此分离超过 4 Å 的发色团，耦合的库仑部分提供了准确的能量分裂。
