Generalization of the periodic LCAO approach in the CRYSTAL code to g-type orbitals

Desmarais, Jacques K.; Erba, Alessandro; Dovesi, Roberto

doi:10.1007/s00214-018-2200-9

Cited by 35 publications

(47 citation statements)

References 8 publications

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“…For the lanthanides, we have used a combined core pseudopotential and Gaussian basis set developed by Erba et al which treats the 4f levels as valence states. 54 In accordance with the previous study on Ln2O3 systems, the oxygen basis set developed by Towler et al was used, with an integration grid consisting of 99 radial points and 1454 angular points. 55 We note that this oxygen basis set was not specifically developed for hyperfine calculations, which need accurate treatment of the core states; more extended oxygen basis sets such as the IGLO-III set were attempted, but resulted in SCF instabilities, presumably arising from the 'mixing' of two basis sets with different qualities.…”

Section: Dftmentioning

confidence: 99%

A 17O paramagnetic NMR study of Sm2O3, Eu2O3, and Sm/Eu-substituted CeO2

Hope

Halat

Lee

et al. 2019

Solid State Nuclear Magnetic Resonance

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Paramagnetic solid-state NMR of lanthanide (Ln) containing materials can be challenging due to the high electron spin states possible for the Ln f electrons, which result in large paramagnetic shifts, and these difficulties are compounded for 17 O due to the low natural abundance and quadrupolar character. In this work, we present examples of 17 O NMR experiments for lanthanide oxides and strategies to overcome these difficulties. In particular, we record and assign the 17 O NMR spectra of monoclinic Sm2O3 and Eu2O3 for the first time, as well as performing density functional theory (DFT) calculations to gain further insight into the spectra. The temperature dependence of the Sm 3+ and Eu 3+ magnetic susceptibilities are investigated by measuring the 17 O shift of the cubic sesquioxides over a wide temperature range, which reveal non-Curie temperature dependence due to the presence of low-lying electronic states. This behaviour is reproduced by calculating the electron spin as a function of temperature, yielding shifts which agree well with the experimental values. Using the understanding of the magnetic behaviour gained from the sesquioxides, we then explore the local oxygen environments in 15 at% Sm-and Eu-substituted CeO2, with the 17 O NMR spectrum exhibiting signals due to environments with zero, one and two nearest neighbour Ln ions, as well as further splitting due to oxygen vacancies. Finally, we extract an activation energy for oxygen vacancy motion in these systems of 0.35 ± 0.02 eV from the Arrhenius temperature dependence of the 17 O T1 relaxation constants, which is found to be independent of the Ln ion within error. The relation of this activation energy to literature values for oxygen diffusion in Ln-substituted CeO2 is discussed to infer mechanistic information which can be applied to further develop these materials as solid-state oxide-ion conductors. Recent efforts by Heinzmann et al. have shown that 17 O NMR (and T1) measurements can be applied to GDC to quantify doping behaviour and to extract activation energy values that can be ascribed to oxideion motion. 41 However, to our knowledge 17 O NMR and/or relaxometry-based techniques have not been used to study conduction in other Ln-substituted CeO2 materials, likely due to the aforementioned difficulties in interpreting NMR spectra of paramagnetic phases. In this work, we apply the lessons learned regarding the magnetic behaviour of Sm 3+ and Eu 3+ as seen in the paramagnetic 17 O NMR of the monoclinic Ln2O3 polymorphs to guide the analysis of variable-temperature 17 O spectra of Sm-and Eu-substituted CeO2.

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Section: Dftmentioning

confidence: 99%

A 17O paramagnetic NMR study of Sm2O3, Eu2O3, and Sm/Eu-substituted CeO2

Hope

Halat

Lee

et al. 2019

Solid State Nuclear Magnetic Resonance

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“…The Gd 4f orbitals are described in the valence by three Gaussians (i.e., “(3f)” notation). The Gd effective valence basis set is [5(sp)2d3f] and contains 36 electrons [ 62 , 63 ]. Moreover, the Hf effective valence basis set is [3(sp)2d] and contains 12 electrons [ 64 ].…”

Section: Methodsmentioning

confidence: 99%

Structural Evolution and Magnetic Properties of Gd2Hf2O7 Nanocrystals: Computational and Experimental Investigations

et al. 2020

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Structural evolution in functional materials is a physicochemical phenomenon, which is important from a fundamental study point of view and for its applications in magnetism, catalysis, and nuclear waste immobilization. In this study, we used x-ray diffraction and Raman spectroscopy to examine the Gd2Hf2O7 (GHO) pyrochlore, and we showed that it underwent a thermally induced crystalline phase evolution. Superconducting quantum interference device measurements were carried out on both the weakly ordered pyrochlore and the fully ordered phases. These measurements suggest a weak magnetism for both pyrochlore phases. Spin density calculations showed that the Gd3+ ion has a major contribution to the fully ordered pyrochlore magnetic behavior and its cation antisite. The origin of the Gd magnetism is due to the concomitant shift of its spin-up 4f orbital states above the Fermi energy and its spin-down states below the Fermi energy. This picture is in contrast to the familiar Stoner model used in magnetism. The ordered pyrochlore GHO is antiferromagnetic, whereas its antisite is ferromagnetic. The localization of the Gd-4f orbitals is also indicative of weak magnetism. Chemical bonding was analyzed via overlap population calculations: These analyses indicate that Hf-Gd and Gd-O covalent interactions are destabilizing, and thus, the stabilities of these bonds are due to ionic interactions. Our combined experimental and computational analyses on the technologically important pyrochlore materials provide a basic understanding of their structure, bonding properties, and magnetic behaviors.

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“…Energies were calculated using periodic density functional theory (DFT), adopting the PBESol and HSE06 functionals , . The atomic Gaussian basis sets used were a 6‐311G* basis set for O, and effective core pseudopotentials (ECP) with valence basis sets for Y, W, and Sm . For the calculation of the Coulomb and exchange integrals, tolerance factors of 7, 7, 7, 7, and 14 were used.…”

Section: Methodsmentioning

confidence: 99%

“…[29,30] The atomic Gaussian basis sets used were a 6-311G* basis set for O, and effective core pseudopotentials (ECP) with valence basis sets for Y, W, and Sm. [31][32][33][34] For the calculation of the Coulomb and exchange integrals, tolerance factors of 7, 7, 7, 7, and 14 were used. The convergence criterion for the electronic energy was set at 10 -7 a.u.…”

Section: Articlementioning

confidence: 99%

The Analyses of Luminescent Properties and Structure of the Tetragonal Phase of Y₂WO₆:Eu³⁺ doped Phosphor

Castillo

Espinoza

Conejeros

et al. 2020

Zeitschrift anorg allge chemie

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The structural, electronic and luminescent properties of the tetragonal phase of Y2WO6 phosphors doped with different amounts of Eu3+ have been studied. All samples were synthesized via solid‐state methods, using NaCl as mineralizer. Through Rietveld refinement was found that the Eu3+ cations only occupy the Y1 (2c) sites of the host‐matrix. The thermal stability of the undoped sample was investigated using simultaneous TG‐DSC thermal analyses. The SEM analysis revealed that the doped and the undoped samples have tendency to form microcrystals with smooth surfaces and in both cases it is possible to observe some agglomerates of nanoparticles. Periodic Density Functional Theory calculations (DFT) were carried out to investigate the electronic properties of the undoped material; these results show good agreement with the experimental ones. The emission spectra of all doped‐samples are dominated by the electric dipole transition (ED) 5D0 → 7F2 located at 613 nm, which indicates that the Eu3+ ions are located in non‐centrosimetric sites in the host‐structure.

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Generalization of the periodic LCAO approach in the CRYSTAL code to g-type orbitals

Cited by 35 publications

References 8 publications

A 17O paramagnetic NMR study of Sm2O3, Eu2O3, and Sm/Eu-substituted CeO2

A 17O paramagnetic NMR study of Sm2O3, Eu2O3, and Sm/Eu-substituted CeO2

Structural Evolution and Magnetic Properties of Gd2Hf2O7 Nanocrystals: Computational and Experimental Investigations

The Analyses of Luminescent Properties and Structure of the Tetragonal Phase of Y₂WO₆:Eu³⁺ doped Phosphor

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Generalization of the periodic LCAO approach in the CRYSTAL code to g-type orbitals

Cited by 35 publications

References 8 publications

A 17O paramagnetic NMR study of Sm2O3, Eu2O3, and Sm/Eu-substituted CeO2

A 17O paramagnetic NMR study of Sm2O3, Eu2O3, and Sm/Eu-substituted CeO2

Structural Evolution and Magnetic Properties of Gd2Hf2O7 Nanocrystals: Computational and Experimental Investigations

The Analyses of Luminescent Properties and Structure of the Tetragonal Phase of Y2WO6:Eu3+ doped Phosphor

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The Analyses of Luminescent Properties and Structure of the Tetragonal Phase of Y₂WO₆:Eu³⁺ doped Phosphor