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#### Zero field splitting of the chalcogen diatomics using relativistic correlated wave-function methods

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##### Citation

Rota, J.-B., Knecht, S., Fleig, T., Ganyushin, D., Saue, T., Neese, F., et al. (2011).
Zero field splitting of the chalcogen diatomics using relativistic correlated wave-function methods.*
The Journal of Chemical Physics,* *135*(11): 114106. doi:10.1063/1.3636084.

Cite as: http://hdl.handle.net/21.11116/0000-0007-FFC4-D

##### 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}.