SPIN POLARIZATION IN RESTRICTED ELECTRONIC-STRUCTURE THEORY - MULTICONFIGURATION SELF-CONSISTENT-FIELD CALCULATIONS OF HYPERFINE COUPLING-CONSTANTS

It is shown that the isotropic hyperfine coupling constant A(iso) associated with the Fermi contact interaction can be accurately calculated from conventional multiconfiguration self-consistent-field wave functions if, in addition to the expectation value of the contact operator, one also includes the terms originating from the response of the wave function. These response terms are nonvanishing only for perturbation operators that are nonsymmetric in spin space. Calculations of A(iso) for N and BH2 illustrate the importance of the_response terms and also indicate that a good estimate of the spin polarization of the core orbitals may be obtained from the response terms without correlating the core.