Manninen Pekka, Ruud Kenneth, Lantto Perttu, Vaara Juha
Laboratory of Physical Chemistry, Department of Chemistry, University of Helsinki, Finland.
J Chem Phys. 2005 Mar 15;122(11):114107. doi: 10.1063/1.1861872.
We present perturbational ab initio calculations of the nuclear-spin-dependent relativistic corrections to the nuclear magnetic resonance shielding tensors that constitute, together with the other relativistic terms reported by us earlier, the full leading-order perturbational set of results for the one-electron relativistic contributions to this observable, based on the (Breit-)Pauli Hamiltonian. These contributions are considered for the H(2)X (X = O,S,Se,Te,Po) and HX (X = F,Cl,Br,I,At) molecules, as well as the noble gas (Ne, Ar, Kr, Xe, Rn) atoms. The corrections are evaluated using the relativistic and magnetic operators as perturbations on an equal footing, calculated using analytical linear and quadratic response theory applied on top of a nonrelativistic reference state provided by self-consistent field calculations. The (1)H and heavy-atom nuclear magnetic shielding tensors are compared with four component, nearly basis-set-limit Dirac-Hartree-Fock calculations that include positronic excitations, as well as available literature data. Besides the easy interpretability of the different contributions in terms of familiar nonrelativistic concepts, the accuracy of the present perturbational scheme is striking for the isotropic part of the shielding tensor, for systems including elements up to Xe.
我们给出了对核磁共振屏蔽张量的核自旋相关相对论修正的微扰从头计算结果。这些修正与我们之前报道的其他相对论项一起，构成了基于（Breit -）泡利哈密顿量的单电子相对论贡献对该可观测量的完整一阶微扰结果集。我们考虑了H₂X（X = O、S、Se、Te、Po）和HX（X = F、Cl、Br、I、At）分子以及稀有气体（Ne、Ar、Kr、Xe、Rn）原子的这些贡献。使用相对论和磁算子作为同等地位的微扰来评估这些修正，通过应用于自洽场计算提供的非相对论参考态之上的解析线性和二次响应理论进行计算。将¹H和重原子核磁共振屏蔽张量与包含正电子激发的四分量、接近基组极限的狄拉克 - 哈特里 - 福克计算结果以及现有的文献数据进行了比较。除了不同贡献在熟悉的非相对论概念方面易于解释之外，对于屏蔽张量的各向同性部分，本微扰方案对于包含直至Xe元素的系统的准确性非常显著。
