title: Zero field splitting of the chalcogen diatomics using relativistic correlated wave-function methods.
abstract: The spectrum arising from the (π*)(2) configuration of the chalcogen dimers, namely, the X(2)1, a2, and b0(+) states, is calculated using wave-function theory based methods. Two-component (2c) and four-component (4c) multireference configuration interaction (MRCI) and Fock-space coupled cluster (FSCC) methods are used as well as two-step methods spin-orbit complete active space perturbation theory at 2nd order (SO-CASPT2) and spin-orbit difference dedicated configuration interaction (SO-DDCI). The energy of the X(2)1 state corresponds to the zero-field splitting of the ground state spin triplet. It is described with high accuracy by the 2- and 4-component methods in comparison with experiment, whereas the two-step methods give about 80% of the experimental values. The b0(+) state is well described by 4c-MRCI, SO-CASPT2, and SO-DDCI, but FSCC fails to describe this state and an intermediate Hamiltonian FSCC ansatz is required. The results are readily rationalized by a two-parameter model; Δε, the π* spinor splitting by spin-orbit coupling and K, the exchange integral between the π(1)* and the π(-1)* spinors with, respectively, angular momenta 1 and -1. This model holds for all systems under study with the exception of Po(2).
authors.affiliation: Laboratoire de Chimie, Ecole Normale Supérieure de Lyon, 46 allée d’Italie 69364 Lyon Cédex 07, France.
authors.forename: J-B
authors.initials: JB
authors.lastname: Rota
authors.forename: S
authors.initials: S
authors.lastname: Knecht
authors.forename: T
authors.initials: T
authors.lastname: Fleig
authors.forename: D
authors.initials: D
authors.lastname: Ganyushin
authors.forename: T
authors.initials: T
authors.lastname: Saue
authors.forename: F
authors.initials: F
authors.lastname: Neese
authors.forename: H
authors.initials: H
authors.lastname: Bolvin