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On the universality of the long-/short-range separation in multiconfigurational density-functional theory. II. Investigating f0 actinide species
Stockholm University, Faculty of Science, Department of Physics. Université Lille 1 (Sciences et Technologies), France.
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
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2009 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, 054107Article in journal (Refereed) Published
Abstract [en]

In a previous paper [ Fromager et al., J. Chem. Phys. 126, 074111 (2007) ], some of the authors proposed a recipe for choosing the optimal value of the μ parameter that controls the long-range/short-range separation of the two-electron interaction in hybrid multiconfigurational self-consistent field short-range density-functional theory (MC-srDFT) methods. For general modeling with MC-srDFT methods, it is clearly desirable that the same universal value of μ can be used for any molecule. Their calculations on neutral light element compounds all yielded μopt = 0.4 a.u. In this work the authors investigate the universality of this value by considering “extreme” study cases, namely, neutral and charged isoelectronic f0 actinide compounds (ThO2, PaO2+, UO22+, UN2, CUO, and NpO23+). We find for these compounds that μopt = 0.3 a.u. but show that 0.4 a.u. is still acceptable. This is a promising result in the investigation of a universal range separation. The accuracy of the currently best MC-srDFT (μ = 0.3 a.u.) approach has also been tested for equilibrium geometries. Though it performs as well as wave function theory and DFT for static-correlation-free systems, it fails in describing the neptunyl (VII) ion NpO23+ where static correlation is significant; bending is preferred at the MC-srDFT (μ = 0.3 a.u.) level, whereas the molecule is known to be linear. This clearly shows the need for better short-range functionals, especially for the description of the short-range exchange. It also suggests that the bending tendencies observed in DFT for NpO23+ cannot be fully explained by the bad description of static correlation effects by standard functionals. A better description of the exchange seems to be essential too.

Place, publisher, year, edition, pages
2009. Vol. 131, 054107
National Category
Physical Sciences
URN: urn:nbn:se:su:diva-54866DOI: 10.1063/1.3187032OAI: diva2:398755
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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