Vibrational corrections to indirect nuclear spin–spin coupling constants calculated by density-functional theory

Abstract

At the present level of electronic-structure theory, the differences between calculated and experimental indirect nuclear spin–spin coupling constants are typically as large as the vibrational contributions to these constants. For a meaningful comparison with experiment, it is therefore necessary to include vibrational corrections in the calculated spin–spin coupling constants. In the present paper, such corrections have been calculated for a number of small molecular systems by using hybrid density-functional theory (DFT), yielding results in good agreement with previous wave-function calculations. A set of empirical equilibrium spin–spin coupling constants has been compiled from the experimentally observed constants and the calculated vibrational corrections. A comparison of these empirical constants with calculations suggests that the restricted-active-space self-consistent field method is the best approach for calculating the indirect spin–spin coupling constants of small molecules, and that the second-order polarization propagator approach and DFT are similar in performance. To illustrate the usefulness of the presented method, the vibrational corrections to the indirect spin–spin coupling constants of the benzene molecule have been calculated.