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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Benchmark Study of Isotropic Hyperfine Coupling Constants for Hydrogen: Influence of Geometry, Correlation Method, and Basis Set
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Benchmark Study of Isotropic Hyperfine Coupling Constants for Hydrogen: Influence of Geometry, Correlation Method, and Basis Set

机译：氢的各向同性超细偶合常数的基准研究：几何，相关方法和基集的影响

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Isotropic hyperfine coupling constants (iHFCCs) can be easily measured by electron spin resonance spectroscopy in solution, but they have proven difficult to calculate from first principles. We test the performance of the newly developed (aug-)cc-pVXZ-t5s basis sets for hydrogen with Dunning's (aug-)cc-pVXZ and -pCVXZ basis sets for non-hydrogen atoms. Correlation is included by CCSD and CCSD(T) using UHF and ROHF references. A two-point extrapolation of cc-pVDZ:cc-pVDZ:cc-pVDZ-t5s-a5 and cc-pVTZ:cc-pVTZ-t5s-a6 hydrogen iHFCCs is found to be very useful. Diffuse functions have nearly no influence on extrapolated iHFCCs. We also explore the dependence of the calculated iHFCCs on the level of theory used in optimizing the geometries. For this purpose, we optimized geometries up to the UHF-CCSD/cc-pCVQZ and UHF-CCSDT/cc-pCVTZ levels and extrapolated to the "complete basis set" limit. The calculated iHFCCs are compared to reference values, which are experimental numbers corrected for solvent and the most important vibrational effects. Our test molecules are the CH_3~·, C_2H_3~·, and H_2CN~· radicals. At the highest level of theory, the largest deviations from the reference values are smaller than 3.5 G and 6%. The rms errors are below 2.1 G and 4%. The cc-pVXZ:cc-pVXZ-t5s basis set combinations perform better than the EPR-n and the Chipman [631|41] basis set. All of them are better than similarly sized basis sets that were not developed for iHFCCs. The calculated iHFCCs are influenced most strongly by the choice of basis set, the perturbative inclusion of connected triple excitations, and the choice of reference wave function and the level of theory in geometry optimization. Core correlation is necessary for the computation of iHFCCs for non-hydrogen atoms but has very little influence on the iHFCCs of hydrogen atoms. A good compromise between the cost and accuracy of hydrogen iHFCCs seems to be reached by two-point extrapolated ROHF-CCSD(T)-fc iHFCCs at UHF-MBPT(2)-fc/cc-pVTZ geometries. ROHF-MBPT(2)-fc or UHF-CCSD-fc/cc-pVTZ geometries are necessary when single excitations are not negligible.
机译：各向同性超精细耦合常数（iHFCC）可以很容易地通过溶液中的电子自旋共振光谱法进行测量，但是事实证明，很难根据第一原理进行计算。我们用Dunning的非氢原子（aug-）cc-pVXZ和-pCVXZ基础集测试了新开发的（aug-）cc-pVXZ-t5s氢基集的性能。 CCSD和CCSD（T）使用UHF和ROHF引用包括相关性。发现cc-pVDZ：cc-pVDZ：cc-pVDZ-t5s-a5和cc-pVTZ：cc-pVTZ-t5s-a6氢iHFCC的两点外推法非常有用。扩散函数对外推iHFCC几乎没有影响。我们还探讨了计算出的iHFCC对优化几何形状所用理论水平的依赖性。为此，我们优化了高达UHF-CCSD / cc-pCVQZ和UHF-CCSDT / cc-pCVTZ的几何形状，并外推到“完整基数”限制。将计算出的iHFCC与参考值进行比较，参考值是针对溶剂和最重要的振动效应校正的实验值。我们的测试分子是CH_3〜·，C_2H_3〜·和H_2CN〜·自由基。在最高理论水平上，与参考值的最大偏差小于3.5 G和6％。均方根误差低于2.1 G和4％。 cc-pVXZ：cc-pVXZ-t5s基集组合的性能优于EPR-n和Chipman [631 | 41]基集。所有这些都比未为iHFCC开发的类似大小的基础集要好。计算的iHFCC受以下因素的影响最大：基础集的选择，相连的三重激发的扰动包含，参考波函数的选择以及几何优化中的理论水平。核心相关性对于非氢原子的iHFCC的计算是必需的，但对氢原子的iHFCC的影响很小。在UHF-MBPT（2）-fc / cc-pVTZ几何结构上，通过两点外推ROHF-CCSD（T）-fc iHFCC似乎可以在氢iHFCC的成本和精度之间取得良好的折衷。当不能忽略单个激发时，需要ROHF-MBPT（2）-fc或UHF-CCSD-fc / cc-pVTZ几何形状。

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