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An Efficient Coupled-Perturbed Kohn-Sham Implementation of NMR Chemical Shift Computations with Local Hybrid Functionals and Gauge-Including Atomic Orbitals.
Journal of Chemical Theory and Computation ( IF 5.5 ) Pub Date : 2020-01-22 , DOI: 10.1021/acs.jctc.9b00944
Caspar Jonas Schattenberg 1 , Kevin Reiter 2 , Florian Weigend 2 , Martin Kaupp 1
Affiliation  

Nuclear shielding calculations for local hybrid (LH) functionals with position-dependent exact-exchange admixtures within a coupled-perturbed Kohn-Sham (CPKS) framework have been implemented into the Turbomole code using efficient seminumerical integration techniques to deal with two-electron integrals. When using gauge-including atomic orbitals, LHs generate additional terms within the "pre-loop" section of the CPKS scheme compared to global hybrid (GH) functionals, related to perturbed electron-repulsion integrals. These terms have been implemented and tested in detail, together with dependencies on grid sizes and integral screening procedures. Even with relatively small grids, a seminumerical treatment of GHs reproduces analytical GH results with high accuracy while improving scaling with system and basis-set sizes significantly. The extra terms generated by LHs in the pre-loop part increase the scaling of that contribution slightly, but the advantages compared to the analytical scheme are largely retained, in particular for the typically large basis sets used in NMR shift calculations, allowing for a very efficient computational scheme. An initial comparison of four first-generation LHs based on LDA exchange for a shielding test set of 15 small main-group molecules against high-level CCSD(T) benchmark data indicates a substantial reduction of the systematically underestimated shieldings compared to semilocal functionals or GHs for non-hydrogen nuclei when a so-called t-LMF is used to control the position dependence of the exact-exchange admixture. In contrast, proton shieldings are underestimated with this LMF, while an LH with a so-called s-LMF performs much better. These results are discussed in the context of experience for other properties, and they suggest directions for further improvements of LHs regarding nuclear shieldings.

中文翻译:

NMR化学位移计算的有效耦合摄动Kohn-Sham实现,具有局部杂化功能和包括原子轨道的量规。

耦合扰动的Kohn-Sham(CPKS)框架内具有位置依赖的精确交换混合物的局部混合(LH)功能的核屏蔽计算已使用有效的半数值积分技术处理Turbomole代码,以处理两电子积分。当使用包括轨距的原子轨道时,与扰动的电子排斥积分有关的全局混合(GH)泛函相比,LH在CPKS方案的“预环”部分中生成了其他项。这些术语已经实现并经过了详细测试,以及对网格大小和整体筛选程序的依赖性。即使使用相对较小的网格,GH的半数值处理也可以高精度再现GH的分析结果,同时显着提高系统和基集大小的缩放比例。LH在回路前部分中生成的额外项会稍微增加该贡献的比例,但与分析方案相比,其优势得以保留,尤其是对于NMR位移计算中使用的通常较大的基集而言,这非常有利有效的计算方案。初步比较了四个基于LDA交换的第一代LH,它们针对15个主要主族小分子的屏蔽测试集与高水平CCSD(T)基准数据进行了比较,表明与半局部功能或GH相比,系统被低估的屏蔽大大减少了当所谓的t-LMF用于控制精确交换混合物的位置相关性时,对于非氢原子核是不适用的。相反,该LMF会低估质子屏蔽,而带有所谓s-LMF的LH的性能要好得多。
更新日期:2020-01-23
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