On the specialization of Gaussian basis sets for core-dependent properties.

Despite the fact that most quantum chemistry basis sets are designed for accurately modeling valence chemistry, these general-purpose basis sets continue to be widely used to model core-dependent properties. Core-specialized basis sets are designed with specific features to accurately represent the behavior of the core region. This design typically incorporates Gaussian primitives with higher exponents to capture core behavior effectively, as well as some decontraction of basis functions to provide flexibility in describing the core electronic wave function. The highest Gaussian exponent and the degree of contraction for both s- and p-basis functions effectively characterize these design aspects. In this study, we compare the design and performance of general-purpose basis sets against several literature-based basis sets specifically designed for three core-dependent properties: J coupling constants, hyperfine coupling constants, and magnetic shielding constants (used for calculating chemical shifts). Our findings consistently demonstrate a significant reduction in error when employing core-specialized basis sets, often at a marginal increase in computational cost compared to the popular 6-31G** basis set. Notably, for expedient calculations of J coupling, hyperfine coupling, and magnetic shielding constants, we recommend the use of the pcJ-1, EPR-II, and pcSseg-1 basis sets, respectively. For higher accuracy, the pcJ-2, EPR-III, and pcSseg-2 basis sets are recommended.