The Basis Set Convergence of Spin-Spin Coupling Constants Calculated by Density Functional Methods.

The previously proposed polarization-consistent basis sets, optimized for density functional calculations, are evaluated for calculating indirect nuclear spin-spin coupling constants. The basis set limiting values can be obtained by performing a series of calculations with increasingly larger basis sets, but the convergence can be significantly improved by adding functions with large exponents. An accurate calculation of the Fermi-contact contribution requires the addition of tight s functions, while the paramagnetic spin-orbit contribution is sensitive to the presence of tight p functions. The spin-dipolar contribution requires the addition of p, d, and f functions. The optimal exponents for the tight functions can be obtained by optimizing the absolute sum of all contributions to the spin-spin coupling constant. On the basis of a series of test cases, we propose a standard set of tight s, p, d, and f functions to be added to the polarization-consistent basis sets. The resulting pcJ-n basis sets should be suitable for calculating spin-spin coupling constants with density functional methods.