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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >A Comparison of Density Functional Methods for the Estimation of Proton Chemical Shifts with Chemical Accuracy
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A Comparison of Density Functional Methods for the Estimation of Proton Chemical Shifts with Chemical Accuracy

机译：用化学精度估算质子化学位移的密度泛函方法的比较

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Fifteen procedures based on hybrid density functional theory were used to calculate magnetic properties for the carbon-bound hydrogen nuclei of 80 small to modest-sized organic molecules. The predicted isotropic shieldings derived from the various methods were compared with each other and also with solution experimental data. The computational methods investigated included the IGAIM and GIAO procedures, the 6-311++G(d,p), 6-311++G(2df,p), and 6-311++G(3df,2p) basis sets, the B3LYP, B3P86, and B3PW91 hybrid density functionals, and molecular geometries optimized using both MP2 and B3LYP methods. Although agreement with experiment consistently improved as the basis set was enlarged, the improvement upon going from 6-311++G(2df,p) to 6-311++G(3df,2p) was extremely small, and even the difference between 6-311++G(d,p) and 6-311++G(2df,p) was of a modest size. The GIAO and IGAIM procedures yielded very similar results in conjunction with the largest basis set, but GIAO suffered considerably less degradation than did IGAIM as the basis set size was decreased. The three functionals B3LYP, B3P86, and B3PW91 performed in an extremely similar fashion, although B3LYP proved marginally superior to the others. The method of geometry optimization also was found to make little difference. Of the computational methods investigated, the GIAO/B3LYP/6-311++G(d,p)/B3LYP/6-31+G(d) procedure probably represents the best compromise between accuracy and expense and yielded proton chemical shifts having a root-mean-square error of 0.15 ppm in comparison with solution experimental values after empirical linear scaling. The more expensive GIAO/B3LYP/6-311++G-(2df,p)/B3LYP/6-31+G(d) method provided only a slightly lower root-mean-square error of 0.14 ppm.
机译：基于混合密度泛函理论的十五种程序被用于计算80个小到中等大小的有机分子的碳结合氢核的磁性。将各种方法得出的预测各向同性屏蔽进行了相互比较，并与溶液实验数据进行了比较。研究的计算方法包括IGAIM和GIAO程序，6-311 ++ G（d，p），6-311 ++ G（2df，p）和6-311 ++ G（3df，2p）基础集，B3LYP，B3P86和B3PW91混合密度泛函以及使用MP2和B3LYP方法优化的分子几何形状。虽然随着基数的增加与实验的一致性不断提高，但是从6-311 ++ G（2df，p）到6-311 ++ G（3df，2p）的改进非常小，甚至6-311 ++ G（d，p）和6-311 ++ G（2df，p）大小适中。结合最大的基集，GIAO和IGAIM程序产生的结果非常相似，但是随着基集大小的减小，GIAO的降解程度要比IGAIM少得多。三个功能B3LYP，B3P86和B3PW91的表现极为相似，尽管事实证明B3LYP略胜于其他功能。还发现几何优化方法几乎没有什么区别。在研究的计算方法中，GIAO / B3LYP / 6-311 ++ G（d，p）/ B3LYP / 6-31 + G（d）程序可能代表了准确性和费用之间的最佳折衷，并产生了具有与经验线性缩放后的溶液实验值相比，均方根误差为0.15 ppm。更为昂贵的GIAO / B3LYP / 6-311 ++ G-（2df，p）/ B3LYP / 6-31 + G（d）方法仅提供了较低的均方根误差0.14 ppm。

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