BASIS-SET DEPENDENCE OF NUCLEAR SPIN-SPIN COUPLING-CONSTANTS

The convergence of NMR indirect spin-spin coupling constants with the extension of the basis set is analyzed, based on calculations carried out at the multiconfigurational self-consistent-field level for the HF and H2O systems. For the dominant and difficult Fermi-contact contrib ution, the standard correlation-consistent basis sets of electronic-st ructure theory are not suitable, lacking flexibility in the core regio n. Improved but not satisfactory convergence of the couplings is obser ved when decontracting the s functions of the correlation-consistent c c-pVXZ basis sets for 2 less than or equal to X less than or equal to 6. Next, by systematically extending these basis sets with tight s fun ctions, new sets are obtained that are sufficiently flexible for accur ate calculations of indirect nuclear spin-spin couplings, without sacr ificing the smooth convergence behavior of the correlation-consistent basis sets.