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首页> 外文期刊>Journal of Computational Chemistry: Organic, Inorganic, Physical, Biological >A Comparison of Quantum Chemical Models for Calculating NMR Shielding Parameters in Peptides:Mixed Basis Set and ONIOM Methods Combined with a Complete Basis Set Extrapolation
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A Comparison of Quantum Chemical Models for Calculating NMR Shielding Parameters in Peptides:Mixed Basis Set and ONIOM Methods Combined with a Complete Basis Set Extrapolation

机译：用于计算肽中NMR屏蔽参数的量子化学模型的比较：混合基础集和ONIOM方法与完整基础集外推相结合

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摘要

This article compares several quantum mechanical approaches to the computation of chemical shielding tensors in peptide fragments.First,we describe the effects of basis set quality up to the complete basis set (CBS) limit and level of theory (HF,MP2,and DFT) for four different atoms in trans N-methylacetamide.For both isotropic shielding and shielding anisotropy,the MP2 results in the CBS limit show the best agreement with experiment.The HF values show quite a different tendency to MP2,and even in the CBS limit they are far from experiment for not only the isotropic shielding of carbonyl carbon but also most shielding anisotropies.In most cases,the DFT values differ systematically from MP2,and small basis-set (double- or triple-zeta) results are often fortuitously in better agreement with the experiment than the CBS ones.Second,we compare the mixed basis set and ONIOM methods,combined with CBS extrapolation,for chemical shielding calculations at a DFT level using various model peptides.From the results,it is shown that the mixed basis set method provides better results than ONIOM,compared to CBS calculations using the nonpartitioned full systems.The information studied here will be useful in guiding the selection of proper quantum chemical models,which are in a tradeoff between accuracy and cost,for shielding studies of peptides and proteins.
机译：本文比较了几种量子力学方法来计算肽片段中化学屏蔽张量的方法。首先，我们描述了基集质量对完整基集（CBS）极限和理论水平（HF，MP2和DFT）的影响。对于反式N-甲基乙酰胺中的四个不同原子。对于各向同性屏蔽和屏蔽各向异性，CBS极限中的MP2结果显示出与实验的最佳一致性.HF值显示MP2的趋势非常不同，甚至在CBS极限中在大多数情况下，DFT值与MP2存在系统性差异，因此，对于DFT值与MP2存在系统性差异，并且较小的基集（双或三Zeta）结果通常要好得多其次，我们比较了混合基集和ONIOM方法，结合CBS外推法，使用各种模型肽在DFT级进行化学屏蔽计算。结果表明，与使用非分区完整系统的CBS计算相比，混合基集方法提供的结果比ONIOM更好。此处研究的信息将有助于指导正确的量子化学模型的选择。在准确性和成本之间进行权衡，以进行肽和蛋白质的屏蔽研究。

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