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On the combined use of discrete solvent models and continuum descriptions of solvent effects in ligand exchange reactions: a case study of the uranyl(VI) aquo ion
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
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2009 (English)In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 124, no 5-6, 377-384 p.Article in journal (Refereed) Published
Abstract [en]

Modeling of the solvent is important when using quantum chemical methods for the assignment of mechanisms from experimental studies of the exchange of water between metal aquo ions and the bulk solvent. In the present study, we have investigated if and how the mechanisms for water exchange in the UO2(OH2)52+–H2O system is affected by the choice of chemical models for the second coordination sphere and physical models for describing the cavity in conductor-like polarizable continuum (CPCM) models. In the first case, we have compared models with one and five waters in the second coordination sphere. For both models, we have compared cavities in which each atom is assigned one spherical cavity and one in which the water molecules are described by a single spherical cavity (the United Atom model). There are significant differences in the relative energy of dissociative and associative intermediates; however, they are not large enough to affect the conclusion that the water exchange proceeds through an associative/interchange mechanism.

Place, publisher, year, edition, pages
2009. Vol. 124, no 5-6, 377-384 p.
Keyword [en]
Actinide, Quantum chemistry, Solvent models, Water exchange
National Category
Physical Sciences
URN: urn:nbn:se:su:diva-54864DOI: 10.1007/s00214-009-0627-8ISI: 000271539400008OAI: diva2:398730
Available from: 2011-02-18 Created: 2011-02-18 Last updated: 2015-07-29Bibliographically approved
In thesis
1. Theoretical Actinide Chemistry – Methods and Models
Open this publication in new window or tab >>Theoretical Actinide Chemistry – Methods and Models
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The chemistry of actinides in aqueous solution is important, and it is essential to build adequate conceptual models and develop methods applicable for actinide systems. The complex electronic structure makes benchmarking necessary. In the thesis a prototype reaction of the water exchange reaction for uranyl(VI), for both ground and luminescent states, described with a six-water model, was used to study the applicability of density functional methods on actinides and different solvation models. An excellent agreement between the wave function methods CCSD(T) and MP2 was obtained in the ground state, implying that near-minimal CASPT2 can be used with confidence for the reaction in the luminescent state of uranyl(VI), while density functionals are not suited to describe energetics for this type of reaction. There was an ambiguity concerning the position of the waters in the second hydration sphere. This issue was resolved by investigating a larger model, and prop- erly used the six-water model was found to adequately describe the water exchange reaction. The effect of solvation was investigated by comparing the results from conductor-like polarizable continuum models using two cavity models. Scattered numbers made it difficult to determine which solvation model to use. The final conclusion was that the water exchange reaction in the luminescent state of uranyl(VI) should be addressed with near-minimal CASPT2 and a solvation model without explicit cavities for hydrogens. Finally it was shown that no new chemistry appears in the luminescent state for this reaction. The thesis includes a methodological investigation of a multi-reference density functional method based on a range separation of the two-electron interaction. The method depends on a universal parameter, which has been determined for lighter elements. It is shown here that the same parameter could be used for actinides, a prerequisite for further development of the method. The results are in that sense promising.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2011. 89 p.
Actinide, Quantum chemistry, Wave function, Density functional theory, Solvent models, Water exchange, Molecular configurations, Multi-reference density functional method
Research subject
Theoretical Physics
urn:nbn:se:su:diva-54848 (URN)978-91-7447-232-5 (ISBN)
Public defence
2011-03-28, FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Available from: 2011-03-06 Created: 2011-02-18 Last updated: 2011-03-16Bibliographically approved

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Wåhlin, PernillaWahlgren, Ulf
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Department of PhysicsNordic Institute for Theoretical Physics (Nordita)
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