Estimation of ionicity coefficients in Li<sub>2</sub>BeF<sub>4</sub> crystals by X-ray diffraction

Seiler, Paul

doi:10.1107/s0108768192009510

Cited by 23 publications

(17 citation statements)

References 13 publications

(20 reference statements)

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“…In our total-energy calculations, the nine closely related potential crystallographic structures are considered. They are, namely, ␣-Li 2 BeH 4 ͑monoclinic; P2 1 / c͒, 10 Cs 2 MgH 4 ͑orthorhombic; Pnma͒, 28 Li 2 BeF 4 ͑trigonal; R-3͒, 29 Na 2 SO 4 ͑trigonal; P-3m1͒, 30 K 2 WO 4 ͑monoclinic; C2/m͒, 31 Ag 2 WO 4 ͑orthorhombic; Pnn2͒, 32 Al 2 MgO 4 ͑cubic; Fd-3m͒, 33 ␣-K 2 ZnBr 4 ͑monoclinic; P2 1 / m͒, 34 and ␤-K 2 ZnBr 4 ͑monoclinic; P2 1 ͒. 34 In order to show how the structure of Li 2 BeH 4 varies under pressure, for each proposed structure, the equilibrium geometry and zero-temperature Gibbs free energy ͑total energy plus PV or enthalpy͒ at more than nine pressure points in the range from 0 to 30.0 GPa are obtained by the complete optimization of the structural parameters, as mentioned above.…”

Section: Resultsmentioning

confidence: 99%

Structural transition ofLi2BeH4under high pressure: A first-principles study

Chen

Wang

et al. 2007

Phys. Rev. B

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We present a systematic first-principles investigation of the high-pressure structural stability of Li 2 BeH 4 . Our total-energy calculations show that at ambient pressure, the structure of ␣-Li 2 BeH 4 observed in experiments is more stable than the other proposed structures in this work and the structural transformation from ␣ to ␤ ͑Cs 2 MgH 4 type; Pnma͒ occurs at 18.1 GPa, together with a volume reduction of 4.7%. A detailed study of their electronic structures under ambient pressure up to 30.0 GPa reveals that this behavior is closely related to the variation in the Be-H covalent bonding in the BeH 4 anionic subunits of Li 2 BeH 4 . Based on a colligated analysis of the covalent bond number per unit area ͑N a ͒ and the scaled bond overlap population ͑BOP s ͒, ␤-NaAlH 4 and ␤-Mg͑AlH 4 ͒ 2 are expected to be the most promising candidates for hydrogen storage among the other investigated materials. However, the improvement of hydrogen absorption and/or desorption for Li 2 BeH 4 is less significant.

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Section: Resultsmentioning

confidence: 99%

Structural transition ofLi2BeH4under high pressure: A first-principles study

Chen

Wang

et al. 2007

Phys. Rev. B

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“…The procedure of constructing nonspherical atomic reference densities was refined further upon introducing a promolecule model constructed from nonspherical atomic densities with “optimized orientation”, and applied thereafter to tackle various problems . Furthermore, ionic instead of neutral atomic densities may be used to construct the promolecule model, although, in some cases, the final produced promolecule density is not sensitive to the selection of either atomic densities …”

Section: Conclusion and Prospectsmentioning

confidence: 99%

Tracing the Fingerprint of Chemical Bonds within the Electron Densities of Hydrocarbons: A Comparative Analysis of the Optimized and the Promolecule Densities

2016

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The equivalence of the molecular graphs emerging from the comparative analysis of the optimized and the promolecule electron densities in two hundred and twenty five unsubstituted hydrocarbons was recently demonstrated [Keyvani et al. Chem. Eur. J. 2016, 22, 5003]. Thus, the molecular graph of an optimized molecular electron density is not shaped by the formation of the C-H and C-C bonds. In the present study, to trace the fingerprint of the C-H and C-C bonds in the electron densities of the same set of hydrocarbons, the amount of electron density and its Laplacian at the (3, -1) critical points associated with these bonds are derived from both optimized and promolecule densities, and compared in a newly proposed comparative analysis. The analysis not only conforms to the qualitative picture of the electron density build up between two atoms upon formation of a bond in between, but also quantifies the resulting accumulation of the electron density at the (3, -1) critical points. The comparative analysis also reveals a unified mode of density accumulation in the case of 2318 studied C-H bonds, but various modes of density accumulation are observed in the case of 1509 studied C-C bonds and they are classified into four groups. The four emerging groups do not always conform to the traditional classification based on the bond orders. Furthermore, four C-C bonds described as exotic bonds in previous studies, for example the inverted C-C bond in 1,1,1-propellane, are naturally distinguished from the analysis.

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“…First, our reference model is an atomic and not an ionic one. Second, the density distributions of even the most strongly ionic compounds such as those of the alkali halides are well-simulated by a superposition of neutral atoms [20] [55] [58]. Note also that, when an atom is nearly spherical (small q-parameter and nearly identical populations of the three p-AOs), then the AO-directions are not well-defined and are physically less significant.…”

Section: Tft Core Parametersmentioning

confidence: 99%

Oriented Nonspherical Atoms in Crystals Deduced from X-Ray Scattering Data

Miller

Jacobson

Ruedenberg

et al. 2001

HCA

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Dedicated to Edgar Heilbronner in honor of his 80th birthday with the authors cordial good wishes A crystallographic pro-molecule/pro-crystal model is described that goes beyond the standard reference model, which explicitly contains only numerically determined atomic positions and thermal vibrational smearings, while leaving all other information lumped together in a so-called deformation density. The new model includes further explicit parameters that identify valence-orbital orientations and occupancies of degenerate or near-degenerate atomic ground states in crystals. A method is described for extracting this additional information as well from X-ray data by least-mean-squares refinements. It is applied to the experimental data sets of three organic molecules: 9-(tert-butyl)anthracene, tetrafluoroterephthalonitrile, and 1,2,3-triazine. The electronic structure inferences are discussed.

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Estimation of ionicity coefficients in Li₂BeF₄ crystals by X-ray diffraction

Cited by 23 publications

References 13 publications

Structural transition ofLi2BeH4under high pressure: A first-principles study

Structural transition ofLi2BeH4under high pressure: A first-principles study

Tracing the Fingerprint of Chemical Bonds within the Electron Densities of Hydrocarbons: A Comparative Analysis of the Optimized and the Promolecule Densities

Oriented Nonspherical Atoms in Crystals Deduced from X-Ray Scattering Data

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Estimation of ionicity coefficients in Li2BeF4 crystals by X-ray diffraction

Cited by 23 publications

References 13 publications

Structural transition ofLi2BeH4under high pressure: A first-principles study

Structural transition ofLi2BeH4under high pressure: A first-principles study

Tracing the Fingerprint of Chemical Bonds within the Electron Densities of Hydrocarbons: A Comparative Analysis of the Optimized and the Promolecule Densities

Oriented Nonspherical Atoms in Crystals Deduced from X-Ray Scattering Data

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Estimation of ionicity coefficients in Li₂BeF₄ crystals by X-ray diffraction