Copper guanidine-quinoline complexes are an important class of bioinorganic complexes that find utilization in electron and atom transfer processes. By substitution of functional groups on the quinoline moiety the electron transfer abilities of these complexes can be tuned. In order to explore the full substitution space by simulations, the accurate theoretical description of the effect of functional groups is essential. In this study, we compare three different methods for the theoretical description of the structures. We use the semi-empirical tight-binding method GFN2-xTB, the density functional TPSSh and the double-hybrid functional B2PLYP. We evaluate the methods on five different complex pairs (Cu(I) and Cu(II) complexes), and compare how well calculated energies can predict the redox potentials. We find even though B2PLYP and TPSSh yield better accordance with the experimental structures. GFN2-xTB performs surprisingly well in the geometry optimization at a fraction of the computational cost. TPSSh offers a good compromise between computational cost and accuracy of the redox potential for real-life complexes.

中文翻译：

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铜 (I/II) 胍-喹啉络合物的氧化还原电位的几何基准和分析：半经验紧束缚和 DFT 方法的比较以及描述实体状态的挑战（第三部分）

铜胍-喹啉配合物是一类重要的生物无机配合物，可用于电子和原子转移过程。通过取代喹啉部分上的官能团，可以调整这些复合物的电子转移能力。为了通过模拟探索完整的替代空间，对官能团的影响进行准确的理论描述是必不可少的。在这项研究中，我们比较了三种不同的结构理论描述方法。我们使用半经验紧束缚方法 GFN2-xTB、密度泛函 TPSSh 和双混合泛函 B2PLYP。我们评估了五种不同的复合物对（Cu(I) 和 Cu(II) 复合物）的方法，并比较了计算能量预测氧化还原电势的能力。我们发现即使 B2PLYP 和 TPSSh 产量更好地符合实验结构。GFN2-xTB 在几何优化方面表现出奇的好，而计算成本却很小。TPSSh 在计算成本和现实生活中复合物氧化还原电位的准确性之间提供了很好的折衷。