Application of the equations-of-motion method to the calculation of the indirect nuclear spin–spin coupling tensors

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Abstract
The equations-of-motion (EOM) method, developed by Rowe and by Shibuya and McKoy as an approach to calculating excitation energies and transition amplitudes relative to a correlated ground state directly, has been extended to the calculation of the indirect nuclear spin–spin coupling tensors. The theoretical values, calculated at ab initio level taking into account all the four electron–nucleus interactions, of a series of saturated and unsaturated molecules, CH4, C2H6, C2H4, C2H2, CN−, HCN, HNC, and HCNH+, correlate satisfactorily with the available experimental data and with corresponding CHF–CI results. The EOM formalism may be therefore a convenient alternative to the time-consuming CHF–CI procedures in order to get reasonable reproduction of the J tensors, even for molecules which suffer from UHF triplet instability in single configuration CHF calculations.