小有机分子化学空间中洪德定则的鲁棒性
Resilience of Hund's rule in the Chemical Space of Small Organic Molecules
AI总结：
本研究通过多种理论方法系统筛查12,880个小有机分子，发现洪德定则普遍成立，未发现真正的S1-T1负能隙，并识别出假阳性案例，共享数据集以促进分子发现。
摘要：
我们致力于在化学空间中识别可能违反洪德定则的小分子。利用十二种TDDFT近似和ADC(2)多体方法，我们报告了bigQM7$\omega$数据集中12,880个闭壳层有机分子（含至多7个CONF原子）的S$_1$和T$_1$激发态能量。在这一全面数据集中，没有任何分子在其最小能量几何构型下，在ADC(2)水平上表现出负的S$_1$-T$_1$能隙，而若干分子显示出小于0.1 eV的能隙值。自旋分量标度双杂化方法SCS-PBE-QIDH与ADC(2)的一致性最佳。然而，在该水平下，少数具有应变$sp^3$-N中心的分子被证明是假阳性，其S$_1$态能量低于T$_1$态。我们研究了一个能隙小于-0.2 eV的原型笼状分子，经更仔细检查后，该分子也被证实为另一个假阳性。我们得出结论：在小闭壳层有机分子的化学空间中，有可能识别出导致S$_1$-T$_1$简并的几何和电子结构特征；尽管如此，没有证据表明存在负能隙。我们将本研究生成的数据集作为模块共享，以通过数据挖掘促进无缝的分子发现。
英文摘要：
We embark on a quest to identify small molecules in the chemical space that can potentially violate Hund's rule. Utilizing twelve TDDFT approximations and the ADC(2) many-body method, we report the energies of S$_1$ and T$_1$ excited states of 12,880 closed-shell organic molecules within the bigQM7$ω$ dataset with up to 7 CONF atoms. In this comprehensive dataset, none of the molecules, in their minimum energy geometry, exhibit a negative S$_1$-T$_1$ energy gap at the ADC($2$) level while several molecules display values $<0.1$ eV. The spin-component-scaled double-hybrid method, SCS-PBE-QIDH, demonstrates the best agreement with ADC(2). Yet, at this level, a few molecules with a strained $sp^3$-N center turn out as false-positives with the S$_1$ state lower in energy than T$_1$. We investigate a prototypical cage molecule with an energy gap $<-0.2$ eV, which a closer examination revealed as another false positive. We conclude that in the chemical space of small closed-shell organic molecules, it is possible to identify geometric and electronic structural features giving rise to S$_1$-T$_1$ degeneracy; still, there is no evidence of a negative gap. We share the dataset generated for this study as a module, to facilitate seamless molecular discovery through data mining.
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