The NMR chemical shifts and indirect spin-spin coupling constants of 12 molecules containing ²⁹Si, ⁷³Ge, ¹¹⁹Sn, and ²⁰⁷Pb [X(CCMe)₄, Me₂X(CCMe)₂, and Me₃XCCH] are presented. The results are obtained from non-relativistic as well as two- and four-component relativistic density functional theory (DFT) calculations. The scalar and spin–orbit relativistic contributions as well as the total relativistic corrections are determined. The main relativistic effect in these molecules is not due to spin–orbit coupling but rather to the scalar relativistic contraction of the s-shells. The correlation between the calculated and experimental indirect spin–spin coupling constants showed that the four-component relativistic density functional theory (DFT) approach using the Perdew’s hybrid scheme exchange-correlation functional (PBE0; using the Perdew-Burke-Ernzerhof exchange and correlation functionals) gives results in good agreement with experimental values. The indirect spin-spin coupling constants calculated using the spin-orbit zeroth order regular approximation together with the hybrid PBE0 functional and the specially designed J-coupling (JCPL) basis sets are in good agreement with the results obtained from the four-component relativistic calculations. For the coupling constants involving the heavy atoms, the relativistic corrections are of the same order of magnitude compared to the non-relativistically calculated results. Based on the comparisons of the calculated results with available experimental values, the best results for all the chemical shifts and non-existing indirect spin–spin coupling constants for all the molecules are reported, hoping that these accurate results will be used to benchmark future DFT calculations. The present study also demonstrates that the four-component relativistic DFT method has reached a level of maturity that makes it a convenient and accurate tool to calculate indirect spin–spin coupling constants of “large” molecular systems involving heavy atoms.

中文翻译：

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Si，Ge，Sn和Pb炔基化合物的NMR参数的相对论效应：标量与自旋轨道效应

包含²⁹ Si，⁷³ Ge，¹¹⁹ Sn和²⁰⁷ Pb的12个分子的NMR化学位移和间接自旋-自旋偶联常数[X（CCMe）₄，Me ₂ X（CCMe）₂和Me ₃[XCCH]。这些结果是从非相对论以及两分量和四分量相对论密度泛函理论（DFT）计算中获得的。确定了标量和自旋轨道的相对论贡献以及总的相对论校正。这些分子的主要相对论效应不是由于自旋-轨道耦合，而是由于s壳的标量相对论收缩。计算的和实验的间接自旋-自旋耦合常数之间的相关性表明，使用Perdew混合方案交换-相关函数（PBE0；使用Perdew-Burke-Ernzerhof交换和相关函数）的四分量相对论密度泛函理论（DFT）方法）得出的结果与实验值非常吻合。使用自旋轨道零阶正则逼近以及混合PBE0函数和经特殊设计的J耦合（JCPL）基组计算的间接自旋-自旋耦合常数与从四分量相对论计算获得的结果非常吻合。对于涉及重原子的耦合常数，相对论校正与非相对论计算结果相比具有相同的数量级。根据计算结果与可用实验值的比较，报告了所有分子的所有化学位移和不存在的间接自旋-自旋偶合常数的最佳结果，希望将这些准确的结果用于基准将来的DFT计算。