Calculation of nuclear spin-spin couplings. X. Analytical derivative method of perturbation energy

The expression for the analytical derivatives of the second-order correlati on energy was derived for a system under the spin-dependent perturbations, and it was applied to the correlated calculation of the (3)J(HH)'s in ethan e, methanol, and methylamine. The calculation showed that the addition of t ight s-type functions to the basis set considerably affects the Fermi conta ct (FC) contribution. Furthermore, the third- and fourth-order correlations were also evaluated for the FC contribution with the finite perturbation t heory. The three noncontact contributions were computed at the Hartree-Fock (HF) level. The total contribution to the (3)J(HH) in ethane was significa ntly lower than the experimental value. The calculated (3)J(HH)'s in methan ol and methylamine were nearer to the experimental couplings than in ethane . (C) 2000 American Institute of Physics. [S0021-9606(00)00208-7].