Charge-Transfer Excitations in Uranyl Tetrachloride ([UO₂Cl₄]^2–): How Reliable are Electronic Spectra from Relativistic Time-Dependent Density Functional Theory?

Abstract

Four-component relativistic time-dependent density functional theory (TD-DFT) is used to study charge-transfer (CT) excitation energies of the uranyl molecule as well as the uranyl tetrachloride complex. Adiabatic excitation energies and vibrational frequencies of the excited states are calculated for the lower energy range of the spectrum. The results for TD-DFT with the CAM-B3LYP exchange-correlation functional for the [UO(2)Cl(4)](2-) system are in good agreement with the experimentally observed spectrum of this species and agree also rather well with other theoretical data. Use of the global hybrid B3LYP gives qualitatively correct results, while use of the BLYP functional yields results that are qualitatively wrong due to the too low CT states calculated with this functional. The applicability of the overlap diagnostic of Peach et al. (J. Chem. Phys.2008, 128, 044118) to identify such CT excitations is investigated for a wide range of vertical transitions using results obtained with three different approximate exchange-correlation functionals: BLYP, B3LYP, and CAM-B3LYP.

Photoelectron spectroscopy and the electronic structure of the uranyl tetrachloride dianion: UO2Cl42−

“…18,19 The uranyl tetrachloride dianion, UO 2 Cl 4 2− , is also an important uranyl complex in the condensed phase and has been the subject of detailed optical spectroscopy and theoretical studies both in the solid state as a Cs 2 UO 2 Cl 4 salt and in solutions. [11][12][13][14][15][20][21][22][23][24][25][26] However, accurate interpretations of the optical spectra of UO 2 Cl 4 2− in the condensed environments remain a challenging task in computational actinide chemistry. 16,18,[26][27][28] For instance, the explanation of the spectroscopic data of crystallized Cs 2 UO 2 Cl 4 still relies on empirical models or approximate qualitative analyses.…”

“…[11][12][13][14][15][20][21][22][23][24][25][26] However, accurate interpretations of the optical spectra of UO 2 Cl 4 2− in the condensed environments remain a challenging task in computational actinide chemistry. 16,18,[26][27][28] For instance, the explanation of the spectroscopic data of crystallized Cs 2 UO 2 Cl 4 still relies on empirical models or approximate qualitative analyses. 25,29 Furthermore, due to prohibitive computational cost, highlevel ab initio quantum chemistry calculations can only be applied to isolated actinyl species, such as UO 2 2+ , UO 2 Cl 4 2− , and NpO 2 Cl 4 2− .…”

Communication: Relativistic Fock-space coupled cluster study of small building blocks of larger uranium complexes

“…This is, however, not an easy task due to the required balanced treatment of both electron correlation and relativistic effects. [4][5][6][7] Several publications [8][9][10][11] underlined the need of highly sophisticated (and computationally expensive) wave function approaches to obtain reliable results. 12,13 Among these, the relativistic intermediate Hamiltonian Fock-space coupled cluster singles and doubles (IH-FSCCSD) method stood out as the most reliable theoretical model.…”

Dissecting the cation–cation interaction between two uranyl units

“…1,2 The [UO 2 ] 2+ building block features short U-O bond lengths (ca. [8][9][10][11][12][13][14][15][16][17][18] Despite its unique characteristics, experimental identification of the [UO 2 ] 2+ unit is often hampered by the coordination of another uranyl ''yl'' oxygen to the actinyl centre. Since the symmetric stretching frequency n 1 (S g + ) in uranyl(VI) is IR-forbidden, in asymmetric surroundings it has a weak absorption signal in the range of 800 to 900 cm À1 .…”