Spectral density analysis of nuclear spin—spin coupling: II. Hartree-Fock LCAO studies for homonuclear coupling constants

A spectral density function has been calculated for the indirect nuclear spin—spin coupling constant for homonuclear coupling. The ground state wavefunction is obtained with a normal ab-initio calculation. The sum over states approach for calculating the reduced coupling constant K is replaced by an integration over a spectral density function where the integration variable is the orbital exponent of a “scanning molecular orbital”. This results in a stable method for calculating K with reasonable accuracy. The spectral density function also gives information about which excited states give important contributions to K.Furthermore a residual spectral density function is defined that can be used as a test for the completeness of a set of virtual orbitals in a sum over states calculation.