Faculty of Chemistry, University of Opole, 48 Oleska Street, 46-052 Opole, Poland.
Institute of Organic Chemistry and Biochemistry of the CAS, Flemingovo nám. 2, 166 10 Prague, Czech Republic.
Molecules. 2022 Nov 25;27(23):8230. doi: 10.3390/molecules27238230.
The quality of theoretical NMR shieldings calculated at the quantum-chemical level depends on various theoretical aspects, of which the basis set type and size are among the most important factors. Nevertheless, not much information is available on the basis set effect on theoretical shieldings of the NMR-active nuclei of the third row. Here, we report on the importance of proper basis set selection to obtain accurate and reliable NMR shielding parameters for nuclei from the third row of the periodic table. All calculations were performed on a set of eleven compounds containing the elements Na, Mg, Al, Si, P, S, or Cl. NMR shielding tensors were calculated using the SCF-HF, DFT-B3LYP, and CCSD(T) methods, combined with the Dunning valence aug-cc-pVZ, core-valence aug-cc-pCVZ, Jensen polarized-convergent aug-pcSseg- and Karlsruhe x2c-Def2 basis set families. We also estimated the complete basis set limit (CBS) values of the NMR parameters. Widely scattered nuclear shieldings were observed for the Dunning polarized-valence basis set, which provides irregular convergence. We show that the use of Dunning core-valence or Jensen basis sets effectively reduces the scatter of theoretical NMR results and leads to their exponential-like convergence to CBS. We also assessed the effect of vibrational, temperature, and relativistic corrections on the predicted shieldings. For systems with single bonds, all corrections are relatively small, amounting to less than 4% of the CCSD(T)/CBS value. Vibrational and temperature corrections were less reliable for HPO and HSiCH due to the high anharmonicity of the molecules. An abnormally high relativistic correction was observed for phosphorus in PN, reaching ~20% of the CCSD(T)/CBS value, while the correction was less than 7% for other tested molecules.
理论 NMR 屏蔽值的量子化学计算质量取决于各种理论方面，其中基组类型和大小是最重要的因素之一。然而，关于基组对第三周期 NMR 活性核理论屏蔽值的影响，信息并不多。在这里，我们报告了正确选择基组对于获得第三周期元素核的准确可靠 NMR 屏蔽参数的重要性。所有计算都是在一组包含 Na、Mg、Al、Si、P、S 或 Cl 元素的 11 种化合物上进行的。使用 SCF-HF、DFT-B3LYP 和 CCSD(T)方法，并结合 Dunning 价 aug-cc-pVZ、核价 aug-cc-pCVZ、Jensen 极化收敛 aug-pcSseg 和 Karlsruhe x2c-Def2 基组族计算 NMR 屏蔽张量。我们还估计了 NMR 参数的完全基组极限 (CBS) 值。对于 Dunning 极化价基组，观察到核屏蔽值广泛分散，这提供了不规则的收敛性。我们表明，使用 Dunning 核价或 Jensen 基组可以有效地减少理论 NMR 结果的分散，并导致它们对 CBS 的指数收敛。我们还评估了振动、温度和相对论修正对预测屏蔽值的影响。对于单键系统，所有修正相对较小，不到 CCSD(T)/CBS 值的 4%。由于分子的高非谐性，对于 HPO 和 HSiCH，振动和温度修正不太可靠。在 PN 中观察到磷的异常高相对论修正，达到 CCSD(T)/CBS 值的约 20%，而对于其他测试分子，修正值小于 7%。
