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Theoretical investigation of the energies and geometries of photoexcited uranyl(VI) ion: A comparison between wave-function theory and density functional theory
Stockholm University, Faculty of Science, Department of Physics.
2007 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 127, no 21, 214302- p.Article in journal (Refereed) Published
Abstract [en]

In order to assess the accuracy of wave-function and density functional theory (DFT) based methods for excited states of the uranyl(VI) UO22+ molecule excitation energies and geometries of states originating from excitation from the sigma(u), sigma(g), pi(u), and pi(g) orbitals to the nonbonding 5f(delta) and 5f(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(u) orbital are symmetric while that arising from excitations out of the pi(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.

Place, publisher, year, edition, pages
2007. Vol. 127, no 21, 214302- p.
Keyword [en]
frequency-dependent polarizabilities; 2nd-order perturbation-theory, electronic-structure calculations, coupled-cluster calculations, correct asymptotic-behavior, quantum-chemical methods, field reference function, transfer excited states, actinyl ions, ab-initio
National Category
Physical Sciences
URN: urn:nbn:se:su:diva-55256DOI: 10.1063/1.2814157ISI: 000251450900013OAI: diva2:402582
authorCount :4Available from: 2011-03-08 Created: 2011-03-07 Last updated: 2011-03-08Bibliographically approved

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