Jahn-Teller and spin-orbit coupling effects in transition-metal trifluorides

The effects of linear and higher-order Jahn-Teller couplings as well as spin-orbit coupling in orbitally degenerate electronic states of the transition-metal trifluorides MnF₃ and CoF₃ have been systematically explored with multi-configuration ab initio methods. The adiabatic potential-energy surfaces of low-lying ⁵E′ and ⁵E″ states have been calculated with the CASSCF method. The spin-orbit coupling is described by matrix elements of the Breit-Pauli operator with nonrelativistic CASSCF wave functions. The Jahn-Teller coupling parameters of the Jahn-Teller active in-plane bending and stretching modes have been determined up to sixth order and fourth order, respectively, in the normal-mode expansion. Vibronic spectra have been computed, employing a Jahn-Teller Hamiltonian up to sixth order in the degenerate bending mode and fourth order in the degenerate stretching mode. These results represent the first ab initio study of the dynamical Jahn-Teller effect in transition-metal trifluorides with inclusion of spin-orbit coupling.