Halogen bond (X‐bond) is a noncovalent interaction between a halogen atom and an electron donor. It is often rationalized by a region of the positive electrostatic potential on the halogen atom, so‐called σ‐hole. The X‐bond strength increases with the atomic number of the halogen involved; thus, for heavier halogens, relativistic effects become of concern. This poses a challenge for the quantum chemical description of X‐bonded complexes. To quantify scalar relativistic effects (SREs) on the interaction energies and σ‐hole properties, we have performed highly accurate coupled‐cluster calculations at the complete basis set limit of several X‐bonded complexes and their halogenated monomers. We found that the SREs are comparable in magnitude to the effect of the basis set. The nonrelativistic calculations typically underestimate the attraction by up to 5% or 23% for brominated and iodinated complexes, respectively. Counterintuitively, the electron densities at the bond critical points are larger for SRE‐free calculations than for the relativistic ones. SREs yield smaller, flatter, and more positive σ‐holes. Finally, we highlight the importance of diffuse functions in the basis sets and provide quantitative arguments for using basis sets with pseudopotentials as an affordable alternative to a more rigorous Douglas‐Kroll‐Hess relativistic theory.

中文翻译：

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标量相对论对卤素键和σ孔性质的影响的评估

卤素键（X键）是卤素原子与电子给体之间的非共价相互作用。通常可以通过卤原子上的正静电势区域（称为σ孔）来合理化。X键强度随所涉及卤素的原子数而增加；因此，对于较重的卤素，相对论效应变得令人关注。这对X键复合物的量子化学描述提出了挑战。量化标量相对论效应（SRE）对相互作用能和σ孔的性质，我们已经在几种X键结合的配合物及其卤代单体的完整基集极限下进行了高度精确的偶联簇计算。我们发现，SRE的规模与基础集的效果相当。非相对论计算通常低估了溴化和碘化络合物的吸引力，最多分别低了5％或23％。与直觉相反，与无相对论的计算相比，无SRE计算的键临界点处的电子密度更大。SRE产生更小，更平坦和更正的σ孔。最后，我们强调了基函数中弥散函数的重要性，并为使用具有伪势的基函数集提供了定量的论据，以作为更严格的道格拉斯·克罗尔·赫斯相对论的可负担的替代方法。