A Fock space coupled cluster study on the electronic structure of the UO2, UO2+, U4+, and U5+ species

Abstract

The ground and excited states of the UO 2 molecule have been studied using a Dirac-Coulomb intermediate Hamiltonian Fock-space coupled cluster approach ͑DC-IHFSCC͒. This method is unique in describing dynamic and nondynamic correlation energies at relatively low computational cost. Spin-orbit coupling effects have been fully included by utilizing the four-component Dirac-Coulomb Hamiltonian from the outset. Complementary calculations on the ionized systems UO 2 + and UO 2 2+ as well as on the ions U 4+ and U 5+ were performed to assess the accuracy of this method. The latter calculations improve upon previously published theoretical work. Our calculations confirm the assignment of the ground state of the UO 2 molecule as a 3 ⌽ 2u state that arises from the 5f 1 7s 1 configuration. The first state from the 5f 2 configuration is found above 10 000 cm −1 , whereas the first state from the 5f 1 6d 1 configuration is found at 5 047 cm −1 .

On the performance of the intermediate Hamiltonian Fock-space coupled-cluster method on linear triatomic molecules: The electronic spectra of NpO2+, NpO22+, and PuO22+

“…The UO 2 molecule has attracted much attention lately since matrix spectroscopy studies indicate that the ground state in a neon matrix could differ from that in an argon matrix. 23,[27][28][29][30] An investigation of UO 2 employing the IHFSCC method and including all relevant configurations ͑5f 1 7s 1 , 5f 2 , 5f 1 6d 1 , and 5f 1 7p 1 ͒ will be reported separately. 23 In Table I, the available experimental values for f 1 NpO 2 2+ are also included.…”

“…23,[27][28][29][30] An investigation of UO 2 employing the IHFSCC method and including all relevant configurations ͑5f 1 7s 1 , 5f 2 , 5f 1 6d 1 , and 5f 1 7p 1 ͒ will be reported separately. 23 In Table I, the available experimental values for f 1 NpO 2 2+ are also included. It should be noted that these absorption spectra were measured in water, 31 but studies in other polar solvents and crystals indicate that the transition energies are not much affected by the environment.…”

“…This cutoff is consistent with our more extensive work on UO 2 that will be reported separately. 23 For the IHFSCC calculations, a partitioning of the P , Q spaces, hereby named "IH-u," was employed for all systems considered. In this partitioning 25 spinors of u symmetry were included in the P space.…”

Study of Actinides by Relativistic Coupled Cluster Methods

“…This has been shown in many benchmark applications of 4-component relativistic CC methods to atoms [11][12][13][14][15][16][17][18] and molecules [19][20][21][22][23][24][25][26][27][28][29][30][31]. The CC method is an all-order, size-extensive, and systematic many-body approach.…”

Efficient quantum chemical valence-only treatments of lanthanide and actinide systems

“…from intermediate Hamiltonian Fock-space coupled cluster (IHFSCC) pseudopotential (DC+B PP) [57] and all-electron (AE DCB) [76] calculations in comparison to experimental data (exp.). The mean absolute error (m.a.e.)…”