Three-dimensional reference interaction site model self-consistent field study of the electronic structure of [Cr(H₂O)₆] ³⁺ in aqueous solution

The three-dimensional reference interaction-site model self-consistent- field (3D-RISM-SCF) method was applied to the electronic structure of hexahydrated chromium trication [Cr(H₂O)₆]³⁺ in aqueous solution. The 3D distribution around [Cr(H₂O) ₆]³⁺ showed 12 maximum density points arising from hydrogen bonds, as well as eight local maximum points at the hollow sites, in the second hydration shell. The 3D distribution function also indicated 20 local maximum sites in the third hydration shell. The low-lying excited states of vertical transitions were computed using time-dependent density functional theory (TD-DFT), including the electric field from the solvent. The electronic configurations and excitation energies calculated using DFT and 3D-RISM-SCF were very similar, although the orbital energies involved in the transition were rather different. The two lowest excited states (1⁴T and 2 ⁴T) were roughly assigned to the d-d transitions, and the third and fourth excited states (3⁴T and 4⁴T) were assigned to ligand-to-metal charge-transfer transitions. The computed excited energies were in good agreement with the experimental values.