Theoretical investigation of the energies and geometries of photoexcited uranyl(VI) ion: A comparison between wave-function theory and density functional theory
- Department of Physics, Stockholm University, AlbaNova University Centre, 106 91 Stockholm (Sweden)
In order to assess the accuracy of wave-function and density functional theory (DFT) based methods for excited states of the uranyl(VI) UO{sub 2}{sup 2+} molecule excitation energies and geometries of states originating from excitation from the {sigma}{sub u}, {sigma}{sub g}, {pi}{sub u}, and {pi}{sub g} orbitals to the nonbonding 5f{sub {delta}} and 5f{sub {phi}} have been calculated with different methods. The investigation included linear-response CCSD (LR-CCSD), multiconfigurational perturbation theory (CASSCF/CASPT2), size-extensivity corrected multireference configuration interaction (MRCI) and AQCC, and the DFT based methods time-dependent density functional theory (TD-DFT) with different functionals and the hybrid DFT/MRCI method. Excellent agreement between all nonperturbative wave-function based methods was obtained. CASPT2 does not give energies in agreement with the nonperturbative wave-function based methods, and neither does TD-DFT, in particular, for the higher excitations. The CAM-B3LYP functional, which has a corrected asymptotic behavior, improves the accuracy especially in the higher region of the electronic spectrum. The hybrid DFT/MRCI method performs better than TD-DFT, again compared to the nonperturbative wave-function based results. However, TD-DFT, with common functionals such as B3LYP, yields acceptable geometries and relaxation energies for all excited states compared to LR-CCSD. The structure of excited states corresponding to excitation out of the highest occupied {sigma}{sub u} orbital are symmetric while that arising from excitations out of the {pi}{sub u} orbitals have asymmetric structures. The distant oxygen atom acquires a radical character and likely becomes a strong proton acceptor. These electronic states may play an important role in photoinduced proton exchange with a water molecule of the aqueous environment.
- OSTI ID:
- 21024551
- Journal Information:
- Journal of Chemical Physics, Vol. 127, Issue 21; Other Information: DOI: 10.1063/1.2814157; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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