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Theoretical investigation of the energies and geometries of photo-excited uranyl(VI) ion: a comparison between wave-function theory and density functional theory

Abstract : In order to assess the accuracy of wave-function and DFT based methods for excited states of the uranyl(VI) UO22+ molecule excitation energies and geometries of states originating from excitation from the σu, σg, πu and πg orbitals to the non-bonding 5fδ and 5fφ 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 density functional theory (DFT) based methods time-dependent density functional theory (TD-DFT) with different functionals and the hybrid DFT/MRCI method. Excellent agreement between all non-perturbative wave-function based methods was obtained. CASPT2 does not give energies in agreement with the non-perturbative 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 non-perturbative 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 σu orbital are symmetric while that arising from excitations out of the πu 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 photo-induced proton exchange with a water molecule of the aqueous environment.
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https://hal.archives-ouvertes.fr/hal-00186596
Contributor : Valérie Vallet Connect in order to contact the contributor
Submitted on : Friday, November 9, 2007 - 6:36:34 PM
Last modification on : Tuesday, October 19, 2021 - 10:59:23 AM

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  • HAL Id : hal-00186596, version 1

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Florent Réal, Valérie Vallet, Ulf Wahlgren, Christel Marian. Theoretical investigation of the energies and geometries of photo-excited uranyl(VI) ion: a comparison between wave-function theory and density functional theory. Journal of Chemical Physics, American Institute of Physics, 2007, 127, pp.214302. ⟨hal-00186596⟩

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