Can DFT Methods be used for Open-shell Actinide Molecules? Comparisons with Multi-configurational Studies including Spin-orbit Coupling of Two Iso-electronic Systems: PuO22+ and PuN2 - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Journal of Chemical Physics Année : 2004

Can DFT Methods be used for Open-shell Actinide Molecules? Comparisons with Multi-configurational Studies including Spin-orbit Coupling of Two Iso-electronic Systems: PuO22+ and PuN2

Résumé

The geometries, electronic structures and vibrational frequencies of two iso-electronic compounds PuO22+ and PuN2 have been studied in detail at the DFT and multi-configurational ab initio levels of theory. Dynamic correlation was taken into account using second-order perturbation theory (CASPT2) and the variational difference-dedicated configuration interaction method (IDDCI), for comparison with the results with those of a DFT study. Spin-orbit effects were included within the framework of an effective uncontracted spin-orbit CI method (EPCISO) which considers electron correlation effects and spin-orbit coupling on equal footing. The twelve lowest f-f electronic transitions are reported. The electronic ground state of both systems is found to be the ? = 4 component of 3Hg. We thus disagree with an earlier assignment of the ground state of PuN2 (E. F. Archibong and A. K. Ray, J. Mol. Struct. (Theochem) 530, 165 (2000)). Spin-orbit effects are small on both the geometry and vibrational frequencies of the ground states of PuO22+ and PuN2, but they completely change the distribution of electronically excited states. A comparison of results obtained with the two classes of methods allows us to demonstrate that an unambiguous assignment of the electronic ground state and electronic spectra requires the use of multi-reference methods including spin-orbit coupling. Single-reference methods such as DFT provide a reasonable description of the electronic properties of ground states of these open-shell systems, and therefore also of their structural and vibrational properties. The experimental antisymmetric stretching frequency of matrix-isolated PuN2 is reproduced well by both CASPT2 and DFT calculations; GGA formulations of DFT are more successful than hybrid versions in this respect. Ground-state properties of UO22+, UN2, UO2, PuO22+ and PuN2 are compared and discussed. The geometries, electronic structures and vibrational frequencies of two iso-electronic compounds PuO22+ and PuN2 have been studied in detail at the DFT and multi-configurational ab initio levels of theory. Dynamic correlation was taken into account using second-order perturbation theory (CASPT2) and the variational difference-dedicated configuration interaction method (IDDCI), for comparison with the results with those of a DFT study. Spin-orbit effects were included within the framework of an effective uncontracted spin-orbit CI method (EPCISO) which considers electron correlation effects and spin-orbit coupling on equal footing. The twelve lowest f-f electronic transitions are reported. The electronic ground state of both systems is found to be the ? = 4 component of 3Hg. We thus disagree with an earlier assignment of the ground state of PuN2 (E. F. Archibong and A. K. Ray, J. Mol. Struct. (Theochem) 530, 165 (2000)). Spin-orbit effects are small on both the geometry and vibrational frequencies of the ground states of PuO22+ and PuN2, but they completely change the distribution of electronically excited states. A comparison of results obtained with the two classes of methods allows us to demonstrate that an unambiguous assignment of the electronic ground state and electronic spectra requires the use of multi-reference methods including spin-orbit coupling. Single-reference methods such as DFT provide a reasonable description of the electronic properties of ground states of these open-shell systems, and therefore also of their structural and vibrational properties. The experimental antisymmetric stretching frequency of matrix-isolated PuN2 is reproduced well by both CASPT2 and DFT calculations; GGA formulations of DFT are more successful than hybrid versions in this respect. Ground-state properties of UO22+, UN2, UO2, PuO22+ and PuN2 are compared and discussed. The geometries, electronic structures and vibrational frequencies of two iso-electronic compounds PuO22+ and PuN2 have been studied in detail at the DFT and multi-configurational ab initio levels of theory. Dynamic correlation was taken into account using second-order perturbation theory (CASPT2) and the variational difference-dedicated configuration interaction method (IDDCI), for comparison with the results with those of a DFT study. Spin-orbit effects were included within the framework of an effective uncontracted spin-orbit CI method (EPCISO) which considers electron correlation effects and spin-orbit coupling on equal footing. The twelve lowest f-f electronic transitions are reported. The electronic ground state of both systems is found to be the ? = 4 component of 3Hg. We thus disagree with an earlier assignment of the ground state of PuN2 (E. F. Archibong and A. K. Ray, J. Mol. Struct. (Theochem) 530, 165 (2000)). Spin-orbit effects are small on both the geometry and vibrational frequencies of the ground states of PuO22+ and PuN2, but they completely change the distribution of electronically excited states. A comparison of results obtained with the two classes of methods allows us to demonstrate that an unambiguous assignment of the electronic ground state and electronic spectra requires the use of multi-reference methods including spin-orbit coupling. Single-reference methods such as DFT provide a reasonable description of the electronic properties of ground states of these open-shell systems, and therefore also of their structural and vibrational properties. The experimental antisymmetric stretching frequency of matrix-isolated PuN2 is reproduced well by both CASPT2 and DFT calculations; GGA formulations of DFT are more successful than hybrid versions in this respect. Ground-state properties of UO22+, UN2, UO2, PuO22+ and PuN2 are compared and discussed. he geometries, electronic structures and vibrational frequencies of two iso-electronic compounds PuO22+ and PuN2 have been studied in detail at the DFT and multi-configurational ab initio levels of theory. Dynamic correlation was taken into account using second-order perturbation theory (CASPT2) and the variational difference-dedicated configuration interaction method (IDDCI), for comparison with the results with those of a DFT study. Spin-orbit effects were included within the framework of an effective uncontracted spin-orbit CI method (EPCISO) which considers electron correlation effects and spin-orbit coupling on equal footing. The twelve lowest f-f electronic transitions are reported. The electronic ground state of both systems is found to be the ? = 4 component of 3Hg. We thus disagree with an earlier assignment of the ground state of PuN2 (E. F. Archibong and A. K. Ray, J. Mol. Struct. (Theochem) 530, 165 (2000)). Spin-orbit effects are small on both the geometry and vibrational frequencies of the ground states of PuO22+ and PuN2, but they completely change the distribution of electronically excited states. A comparison of results obtained with the two classes of methods allows us to demonstrate that an unambiguous assignment of the electronic ground state and electronic spectra requires the use of multi-reference methods including spin-orbit coupling. Single-reference methods such as DFT provide a reasonable description of the electronic properties of ground states of these open-shell systems, and therefore also of their structural and vibrational properties. The experimental antisymmetric stretching frequency of matrix-isolated PuN2 is reproduced well by both CASPT2 and DFT calculations; GGA formulations of DFT are more successful than hybrid versions in this respect. Ground-state properties of UO22+, UN2, UO2, PuO22+ and PuN2 are compared and discussed.
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Dates et versions

hal-00003399 , version 1 (29-11-2004)

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  • HAL Id : hal-00003399 , version 1

Citer

Colin J. Marsden, Carine Clavaguéra-Sarrio, Valérie Vallet, Daniel Maynau. Can DFT Methods be used for Open-shell Actinide Molecules? Comparisons with Multi-configurational Studies including Spin-orbit Coupling of Two Iso-electronic Systems: PuO22+ and PuN2. Journal of Chemical Physics, 2004, 121, pp.5312. ⟨hal-00003399⟩
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