Structure and spectroscopy of Pa4+ defects in Cs2ZrCl6. An ab initio theoretical study

Abstract

In this paper we present the results of spin-orbit relativistic ab initio model potential embedded cluster calculations on (PaCl 6 ) 2Ϫ embedded in a reliable representation of the Cs 2 ZrCl 6 host. Totally symmetric local distortions and vibrational frequencies are calculated for all the states of the 5 f 1 and 6d 1 manifolds, as well as the corresponding 5 f ↔6d transition energies and the shape of the 5 f (⌫ 8u )←6d(⌫ 8g ) fluorescence band. An excellent overall agreement with available experimental data is observed which allows us to conclude that the quality of the spin-orbit operators used is very high for actinide elements, as was already known for transition metal and lanthanide elements. Furthermore, it is concluded that the structural and spectroscopic information produced here is very reliable and that the 6d(⌫ 8g Ј ) state is around 10 000 cm Ϫ1 higher in energy than it was thought; our calculations suggest a value of 30 000 cm Ϫ1 for the 10Dq parameter of Pa 4ϩ in Cs 2 ZrCl 6 , which would be compatible with the lower limit of 20 000 cm Ϫ1 accepted for Ce 3ϩ in Cs 2 NaYCl 6 .

Charge Transfer in Uranyl(VI) Halides [UO2X4]2− (X = F, Cl, Br, and I). A Quantum Chemical Study of the Absorption Spectra

“…The AIMP method has been successfully used in many applications related to structural and spectroscopic properties of impurities in solids. [33][34][35][36][37] When the AIMPs are used in the present context it is no longer necessary to have symmetry independent ligands, and thus we have performed the calculations in the higher C 2v symmetry.…”

Quantum chemical study of the lanthanide bond length contraction on Ln3+-doped Cs2NaYCl6 crystals (Ln=Ce to Lu)

“…[1][2][3] As a consequence of this lack of structural information and together with the fact that the band shapes depend on the square of the bond length offsets between the initial and final electronic states, but not on their sign, it has been widely accepted that the bond distances in Ln and An doped crystals are larger in the f nϪ1 d 1 energy levels than in the case of the f n configuration, 4 -7 even when this idea has been neither confirmed nor rejected from experiments. On the contrary, it has been contradicted by a number of solid state quantum chemistry works on Ln and An ions in halide crystals [8][9][10][11] and has been specifically adressed and interpreted using quantum chemistry methods for the analysis of the bonding in Ref. 12.…”

“…The third term is the core shifting operator of Huzinaga and Cantu 32 that prevents the valence orbitals from collapsing onto the core orbitals. It has been recently demonstrated that spin-orbit coupling does not affect structural parameters like the ones which are the goal of this work [8][9][10] and it is for this reason that spin-orbit terms have been omitted in the AIMP embedded cluster Hamiltonian.…”

“…37; it has been used to study the structure and spectroscopy of transition metal ion impurities at ambient and high pressures, 37,39 and lanthanide/actinide ion impurities. [8][9][10][11] The MOLCAS-5 program system 40 was used to compute the embedded cluster wave functions and energies.…”

“…However, this distortion could be difficult to evaluate from an experimental point of view, as it would require EXAFS measurements, which demand the use of synchrotron radiation facilities not readily available for all experimenters. 20 The required lanthanide-ligand distances R i can be obtained directly from quantum chemical calculations on the Ln 3ϩ defects in a particular host crystal, as it has been recently demonstrated, [8][9][10] and, therefore, an important objective of this paper is to calculate the equilibrium geometry of the electronic ground state of the Cs 2 NaYCl 6 :(LnCl 6 ) 3Ϫ embedded clusters. This alternative, apart from providing the local structure parameters ͑i.e., bond lengths and symmetric bond stretching vibrational frequencies͒, and their variation across the lanthanide series, could enable an interesting combination of the Judd-Morrison model with ab initio embedded cluster models of quantum chemistry.…”