title: Communication: spin-orbit splittings in degenerate open-shell states via Mukherjee's multireference coupled-cluster theory: a measure for the coupling contribution.
abstract: We propose a generally applicable scheme for the computation of spin-orbit (SO) splittings in degenerate open-shell systems using multireference coupled-cluster (MRCC) theory. As a specific method, Mukherjee's version of MRCC (Mk-MRCC) in conjunction with an effective mean-field SO operator is adapted for this purpose. An expression for the SO splittings is derived and implemented using Mk-MRCC analytic derivative techniques. The computed SO splittings are found to be in satisfactory agreement with experimental data. Due to the symmetry properties of the SO operator, SO splittings can be considered a quality measure for the coupling between reference determinants in Jeziorski-Monkhorst based MRCC methods. We thus provide numerical insights into the coupling problem of Mk-MRCC theory.
authors.affiliation: Institut für Physikalische Chemie, Universität Mainz, D-55099 Mainz, Germany. MueckL@uni-mainz.de
authors.forename: Leonie Anna
authors.initials: LA
authors.lastname: Mück
authors.forename: Jürgen
authors.initials: J
authors.lastname: Gauss
mesh_terms: D011789:Quantum Theory