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

The expression for the analytical derivatives of the second-order correlation energy was derived for a system under the spin-dependent perturbations, and it was applied to the correlated calculation of the [sup 3]J[sub HH]'s in ethane, methanol, and methylamine. The calculation showed that the addition of tight s-type functions to the basis set considerably affects the Fermi contact (FC) contribution. Furthermore, the third- and fourth-order correlations were also evaluated for the FC contribution with the finite perturbation theory. The three noncontact contributions were computed at the Hartree-Fock (HF) level. The total contribution to the [sup 3]J[sub HH] in ethane was significantly lower than the experimental value. The calculated [sup 3]J[sub HH]'s in methanol and methylamine were nearer to the experimental couplings than in ethane. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]