ABINITIO QUADRATIC CONFIGURATION-INTERACTION CALCULATIONS OF ISOTROPIC HYPERFINE COUPLING-CONSTANTS

Results are presented from quadratic configuration interaction (QCISD) calculations of the isotropic component of the magnetic hyperfine coupling in the electronic ground states of the atoms B-F and of some radicals and radical cations derived from associated diatomic hydrides. Moderately large basis sets of contracted Gaussian functions are employed. Starting from unrestricted Hartree-Fock (UHF) reference spaces the unpaired spin density is determined by finite Fermi contact field perturbation theory. Comparison is made with previous values obtained an approximate augmented coupled-cluster procedure in which both single and triple excitations are handled perturbatively. In all cases the QCISD predictions lie closer to the available experimentally observed hypefine splittings.