Institut für Physikalische Chemie, Universität Mainz, D-55099 Mainz, Germany.
J Chem Phys. 2010 Feb 14;132(6):064109. doi: 10.1063/1.3310282.
High-level ab initio benchmark calculations of the (15)N and (31)P NMR chemical shielding constants for a representative set of molecules are presented. The computations have been carried out at the Hartree-Fock self-consistent field (HF-SCF), density functional theory (DFT) (B-P86 and B3-LYP), second-order Moller-Plesset perturbation theory (MP2), coupled cluster singles and doubles (CCSD), and CCSD augmented by a perturbative treatment of triple excitations [CCSD(T)] level of theory using basis sets of triple zeta quality or better. The influence of the geometry, the treatment of electron correlation, as well as basis set and zero-point vibrational effects on the shielding constants are discussed and the results are compared to gas-phase experimental shifts. As for the first time a study using high-level post-HF methods is carried out for a second-row element, we also propose a family of basis sets suitable for the computation of (31)P shielding constants. The mean deviations observed for (15)N and (31)P are 0.9 [CCSD(T)/13s9p4d3f] and -3.3 ppm [CCSD(T)/15s12p4d3f2g], respectively, when corrected for zero-point vibrational effects. Results obtained at the DFT level of theory are of comparable accuracy to MP2 for (15)N and of comparable accuracy to HF-SCF for (31)P. However, they are not improved by inclusion of zero-point vibrational effects. The PN molecule is an especially interesting case with exceptionally large electron correlation effects on shielding constants beyond MP2 which, therefore, represents an excellent example for further benchmark studies.
呈现了一组具有代表性的分子的（15）N 和（31）P NMR 化学位移常数的高水平从头算基准计算。这些计算是在哈特利-福克自洽场（HF-SCF）、密度泛函理论（DFT）（B-P86 和 B3-LYP）、二级 Møller-Plesset 微扰理论（MP2）、耦合簇单双激发（CCSD）以及通过微扰处理三重激发[CCSD(T)]理论水平进行的，使用三重 zeta 质量或更好的基组。讨论了几何形状、电子相关处理以及基组和零点振动效应对屏蔽常数的影响，并将结果与气相实验位移进行了比较。由于首次对第二周期元素进行了使用高级后 Hartree-Fock 方法的研究，我们还提出了一系列适合计算（31）P 屏蔽常数的基组。当考虑零点振动效应时，（15）N 和（31）P 的平均偏差分别为 0.9（CCSD(T)/13s9p4d3f）和-3.3 ppm（CCSD(T)/15s12p4d3f2g）。DFT 理论水平的结果对于（15）N 的精度与 MP2 相当，对于（31）P 的精度与 HF-SCF 相当。然而，通过包含零点振动效应，它们的精度并没有提高。PN 分子是一个特别有趣的例子，其屏蔽常数的电子相关效应超出了 MP2，因此，它是进一步基准研究的一个极好的例子。
