The molecular structure of AgBr _2 and AgBr _2 ~+. A benchmark CASSCF, CASPT2, and averaged coupled pair functional study

摘要

The ground states of AgBr _2 and AgBr _2 ~+ have been predicted to be B _2~2 and A _1~1 bent structures (θ = 67 ~° and θ = 47 ~°, respectively) using complete active space self-consistent field (CASSCF) and multireference second order perturbation theory (J. Chem. Phys., 1999, 111, 8925). Because CuF _2, CuCl _2, and AgCl _2 are known to be linear, the ground states of AgBr _2 and AgBr _2 ~+ have been studied through benchmark ab initio CASSCF(21,15), multireference second-order perturbation theory and averaged coupled pair functional calculations using very large and especially developed valence basis sets. The bent nature of the ground state of the AgBr _2 ~+ ion is confirmed, but for AgBr _2 the absolute minimum of the ground state is found to be π _g~2 in the linear centrosymmetric structure with the present large optimized basis sets at all levels of theory. Also, a significant Ag-Br bond length reduction was obtained for the cation with respect to the previous value. These results show the crucial role played by the quality of the valence atomic basis sets for this type of transition metal molecules on key properties such as the equilibrium geometry. New equilibrium geometries, vibrational frequencies and ionization potentials are presented.