title: Electron spin-spin coupling from multireference configuration interaction wave functions.
abstract: We present the implementation of two-electron spin-spin coupling as a quasidegenerate perturbative treatment of the Breit-Pauli spin-spin Hamiltonian. The evaluation is based on a multireference CI treatment and constitutes one of the first efforts in the calculation of this effect within a highly sophisticated consideration of both nondynamical and dynamical correlation. The extension of existing schemes for efficient calculation, in particular, of the spin-coupling elements necessitated some involved derivations, the outline of which is presented herein. Application of the program to calculations of diagonal as well as off-diagonal spin-coupling elements is illustrated with the test cases O(2) and NH.
authors.affiliation: Department of Theoretical and Computational Chemistry, University of Düsseldorf, Germany.
authors.forename: Natalie
authors.initials: N
authors.lastname: Gilka
authors.forename: Peter R
authors.initials: PR
authors.lastname: Taylor
authors.forename: Christel M
authors.initials: CM
authors.lastname: Marian