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The correlation consisten basis sets developed by Dunning et. al. are augmented and optimized for the calculation of indirect spin-spin
coupling constants. It is well known, that while values close to the basis set limit can be obtained by performing a series of calculations with increasing basis set size, the convergence of the results can be significantly improved by adding functions with tight exponents if indirect nuclear spin-spin couplings are regarded. A closer investigation exhibits that 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. In our work, the optimal exponents for the tight functions were obtained by optimizing the absolute sum of all contributions to the spin-spin coupling constant, following the scheme suggested by F. Jensen for the polarization consistent (PC-J) basis sets. On the basis of a series of test cases, we propose a standard set of tight s-, p-, d-, and f-functions to be used for augmenting Dunning's correlation consistent basis sets. The resulting UNC-pVXZ-J basis sets (X = D,T,Q and 5) are suitable for calculating spin-spin coupling constants with post HF-correlation methods like coupled cluster or perturbation theory for larger systems, as the number of basis functions required for highly accurate results is decreased drastically in comparison to the uncontracted Dunning basis sets. |
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