Important components for accurate hyperfine coupling constants: electron correlation, dynamic contributions, and solvation effects

The calculation of hyperfine coupling constants is a challenging task in balancing accuracy and computational effort. While previous work has shown the importance of electron correlation and molecular dynamic contributions, we present a systematic study simultaneously analyzing the influence of both effects on hyperfine coupling constants. To this end, we thoroughly study two organic radicals, namely the dimethylamino radical and ethanal radical cation, proving the need to account for conformational flexibility as well as the large influence of electron correlation. Based on these results, we analyse the effect of electron correlation and dynamic simulations on a set of 12 organic radicals, illustrating that both effects are vital for an accurate in silico description on the same scale. Furthermore, we study the influence of solvation using the efficient nuclei-selected algorithm to obtain hyperfine coupling constants with electron correlation for large systems, indicating the necessity to include explicit solvent molecules. Finally, we introduce a composite approach to incorporate all contributions for hyperfine coupling of radicals in solution at comparatively low computational cost. This is successfully tested on the hydroxylated TEMPO radical in aqueous solution, where we are able to compute a 14N-HFCC of 44.4 MHz compared to the experimentally measured 47.6 MHz.

超精细耦合常数（hyperfine coupling constants, HFCC）的计算，是平衡计算精度与计算成本之间的一项极具挑战性的任务。尽管已有研究表明电子相关效应（electron correlation）与分子动力学贡献（molecular dynamic contributions）的重要性，本研究开展了一项系统性工作，同时分析这两种因素对超精细耦合常数的影响。为此，我们深入研究了两种有机自由基（organic radicals）：二甲基氨基自由基（dimethylamino radical）与乙醛自由基阳离子（ethanal radical cation），证实了需要考虑构象灵活性（conformational flexibility）以及电子相关效应的显著影响。基于上述结果，我们针对12种有机自由基组成的数据集，分析了电子相关效应与动力学模拟的影响，结果表明这两种因素对于同一尺度下精准的计算机模拟（in silico）描述至关重要。此外，我们采用高效的核选择算法（nuclei-selected algorithm），针对大体系计算考虑电子相关效应的超精细耦合常数，以此研究溶剂化效应（solvation）的影响，结果表明必须纳入显式溶剂分子（explicit solvent molecules）。最后，我们提出了一种复合方法（composite approach），能够以相对较低的计算成本，整合溶液中自由基超精细耦合的所有贡献项。该方法在水溶液（aqueous solution）中的羟基化TEMPO自由基（hydroxylated TEMPO radical）上得到了成功验证：我们计算得到的14N超精细耦合常数（14N-HFCC）为44.4 MHz，与实验测量的47.6 MHz数值相符。