Partitioned equation-of-motion coupled cluster approach to indirect nuclear spin-spin coupling constants

Two approximations to equation-of-motion coupled cluster theory for second-order properties are introduced that increase the computational efficiency of the approach without forsaking the accuracy of the method. Using partitioning techniques the doubles-doubles block in the EOM Hamiltonian is replaced by a diagonal approximation, and in addition the CCSD ground state may be replaced by its analog from first-order perturbation theory. It is shown that partitioning hardly affects the accuracy of the approach. The Fermi contact contribution to the coupling constant is found to be most sensitive to the inclusion of ground state correlation.