Relativistic effects on the nuclear magnetic resonance shielding of FX (X = F, Cl, Br, I, and At) molecular systems

We present ab inito full four-component and spin-free calculations of the NMR shielding parameter, σ, in the FX (X = F, Cl, Br, I and At) molecular systems. A different expression that overcomes the traditional non-relativistic (NR) approximation used to calculate the relationship between spin-rotation constants and the paramagnetic terms of σ p are given. Large deviations from NR results are obtained for σ(X; X = I and At) and for σ(F; FAt). \documentclass[12pt]{minimal}\begin{document}$\sigma _{\parallel }^p$\end{document} σ ∥ p (I; FI) is zero within the NR approach but −447.4 parts per million from our calculations. The electronic origin of relativistic corrections are analyzed. All passive SO contributions are obtained as a difference between full four-component calculations and spin-free ones. Considering relativistic effects on the anisotropy, we obtain a deviation of 10% for I and 25% for At. \documentclass[12pt]{minimal}\begin{document}$\sigma _{\parallel }^{SO}$\end{document} σ ∥ S O (X) is always negative and \documentclass[12pt]{minimal}\begin{document}$\sigma _{\parallel }^{SF}$\end{document} σ ∥ S F (X) is always positive; the passive SO becomes larger than the SF one for X = Br, I, and At. Both \documentclass[12pt]{minimal}\begin{document}$\sigma _{\parallel }^{SO}$\end{document} σ ∥ S O (X) and \documentclass[12pt]{minimal}\begin{document}$\sigma _{\perp }^{SO}$\end{document} σ ⊥ S O (X) have a functional dependence such as a \documentclass[12pt]{minimal}\begin{document}${\rm Z}_X^b$\end{document} Z X b being the exponent 3.5 and 3.65, respectively. The passive SO contribution to the anisotropy has a similar functional dependence with an exponent of 3.60, meaning that its perpendicular component is larger than its corresponding parallel component.