New operators for calculation of indirect nuclear spin-spin coupling constants

The Fermi contact interaction, which makes an important contribution to indirect nuclear spin-spin coupling constants, is sensitive to the electronic behavior at the positions of the coupled nuclei. Unfortunately, these regions are often not described well in commonly used molecular wave functions. It is shown that the delta function operators which formally represent this interaction in such second-order properties can be replaced by certain global operators in a manner analogous to that previously derived for first-order properties. It is further argued that two specific choices of the new operators that have previously been demonstrated to be very useful for the calculation of isotropic hyperfine coupling constants may also be valuable in improving the accuracy of indirect nuclear spin-spin coupling constant calculations. Illustrative calculations are presented for HD withencouraging results. (C) 1997 American Institute of Physics.