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首页> 美国卫生研究院文献>The Journal of Chemical Physics >Intermolecular shielding contributions studied by modeling the 13C chemical-shift tensors of organic single crystals with plane waves
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Intermolecular shielding contributions studied by modeling the 13C chemical-shift tensors of organic single crystals with plane waves

机译：通过用平面波模拟有机单晶的13C化学位移张量研究分子间屏蔽作用

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In order to predict accurately the chemical shift of NMR-active nuclei in solid phase systems, magnetic shielding calculations must be capable of considering the complete lattice structure. Here we assess the accuracy of the density functional theory gauge-including projector augmented wave method, which uses pseudopotentials to approximate the nodal structure of the core electrons, to determine the magnetic properties of crystals by predicting the full chemical-shift tensors of all 13C nuclides in 14 organic single crystals from which experimental tensors have previously been reported. Plane-wave methods use periodic boundary conditions to incorporate the lattice structure, providing a substantial improvement for modeling the chemical shifts in hydrogen-bonded systems. Principal tensor components can now be predicted to an accuracy that approaches the typical experimental uncertainty. Moreover, methods that include the full solid-phase structure enable geometry optimizations to be performed on the input structures prior to calculation of the shielding. Improvement after optimization is noted here even when neutron diffraction data are used for determining the initial structures. After geometry optimization, the isotropic shift can be predicted to within 1 ppm.
机译：为了准确预测固相系统中NMR活性核的化学位移，磁屏蔽计算必须能够考虑完整的晶格结构。在这里，我们评估密度泛函理论量规（包括投影仪增强波方法）的准确性，该方法使用伪势来近似核心电子的节点结构，并通过预测所有的全化学位移张量来确定晶体的磁性。先前已报道过实验张量的14种有机单晶中的> 13 C核素。平面波方法使用周期性边界条件并入晶格结构，为建模氢键体系中的化学位移提供了实质性的改进。现在可以将主要张量分量预测为接近典型实验不确定性的精度。而且，包括全固相结构的方法使得能够在计算屏蔽之前在输入结构上执行几何优化。即使将中子衍射数据用于确定初始结构，也要注意优化后的改进。经过几何优化后，各向同性位移可以预测在1 ppm以内。

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