Theoretical study of the electronic structure of covalent solids

1991 ◽  
Vol 69 (6) ◽  
pp. 720-725 ◽  
Author(s):  
D. C. Khan ◽  
P. K. Khowash
Keyword(s):  
Experimental Data ◽  
Electronic Structure ◽  
Charge Transfer ◽  
Crystal Field ◽  
Chemical Bonding ◽  
Theoretical Study ◽  
Energy Spectra ◽  
X Ray ◽  
The One ◽  
A Charge

The aim of this work is to study theoretically the electronic structure of a number of ionic and covalent solids. The charges within each atomic region are calculated and a charge-transfer diagram is introduced to define a measure of the chemical bonding (ionic and (or) covalent) in these systems. The crystal-field splitting, 10 Dq, is determined for crystals with a 3d cation from the one-electron energy spectra and compared with available experiments. The transition between two of the valence levels is calculated wherever the corresponding X-ray photoelectron spectrometry or optical spectroscopic experimental data exist in the literature. Finally, the Mössbauer isomer shifts are calculated for iron containing samples.

Determining Crystal Field Distortions of YVO3 through X-Ray Scattering

2009 ◽  
Vol 152-153 ◽  
pp. 147-150
Author(s):  
Thomas A.W. Beale ◽  
Roger D. Johnson ◽  
Stewart R. Bland ◽  
Peter D. Hatton ◽  
Laurence Bouchenoir ◽  
...  
Keyword(s):  
Experimental Data ◽  
Crystal Field ◽  
Energy Spectra ◽  
Resonant Energy ◽  
X Ray ◽  
X Ray Scattering ◽  
Anisotropic Tensor ◽  
Ray Scattering

We present resonant x-ray scattering experimental data from YVO3. By scattering at the vanadium K edge we are able to observe diffraction from the anisotropic tensor of susceptibility at the Bragg forbidden (010). The resonant energy spectra from these reflections are unusually complex, giving an indication of the crystal field distortions around the vanadium site.

scholarly journals Unbinding of Hyaluronan Accelerates the Enzymatic Activity of Bee Hyaluronidase

2011 ◽  
Vol 286 (41) ◽  
pp. 35699-35707 ◽  
Author(s):  
Attila Iliás ◽  
Károly Liliom ◽  
Brigitte Greiderer-Kleinlercher ◽  
Stephan Reitinger ◽  
Günter Lepperdinger
Keyword(s):  
Experimental Data ◽  
Quartz Crystal ◽  
Surface Loop ◽  
X Ray ◽  
Site Model ◽  
Substrate Interaction ◽  
Close Proximity ◽  
Binding Groove ◽  
The One ◽  
Best Fit

Hyaluronan (HA), a polymeric glycosaminoglycan ubiquitously present in higher animals, is hydrolyzed by hyaluronidases (HAases). Here, we used bee HAase as a model enzyme to study the HA-HAase interaction. Located in close proximity to the active center, a bulky surface loop, which appears to obstruct one end of the substrate binding groove, was found to be functionally involved in HA turnover. To better understand kinetic changes in substrate interaction, binding of high molecular weight HA to catalytically inactive HAase was monitored by means of quartz crystal microbalance technology. Replacement of the delimiting loop by a tetrapeptide interconnection increased the affinity for HA up to 100-fold, with a KD below 1 nm being the highest affinity among HA-binding proteins surveyed so far. The experimental data of HA-HAase interaction were further validated showing best fit to the theoretically proposed sequential two-site model. Besides the one, which had been shown previously in course of x-ray structure determination, a previously unrecognized binding site works in conjunction with an unbinding loop that facilitates liberation of hydrolyzed HA.

scholarly journals Chemical Bonding and the Sulfur K X-Ray Spectrum

1965 ◽  
Vol 9 ◽  
pp. 354-364 ◽  
Author(s):  
D. W. Wilbur ◽  
J. W. Gofman
Keyword(s):  
Electronic Structure ◽  
Single Crystal ◽  
Organic Compounds ◽  
Sulfur Atom ◽  
Chemical Bonding ◽  
Proportional Counter ◽  
Pulse Height ◽  
X Ray ◽  
Pulse Height Analysis ◽  
Chemical States

AbstractAn investigation has been made of the relative Kβ intensities in different chemical states of the sulfur atom using the Kα lines, with appropriate corrections, to provide the intensity standards. Both inorganic and organic compounds were included in the study. The data for each compound appear to be reliable to about ± 0.5%, while the whole series of compounds shows a variation greater than 20% in the corrected Kβ/Kα ratios. Energies were also measured, particularly the Kα energies, and their shifts were studied relative to the Kβ, intensity shifts. The work was done with a plane, single-crystal, helium-path spectrometer with proportional counter and pulse-height analysis for detection. The results are indicative of the usefulness of the method both in clarifying an uncertain chemical state and in studying the electronic structure of the bonded atom.

scholarly journals Энергетический спектр и оптическое поглощение эндоэдральных комплексов Er-=SUB=-2-=/SUB=-C-=SUB=-2-=/SUB=-@C-=SUB=-90-=/SUB=- на основе изомеров N 21 и N 44

2021 ◽  
Vol 129 (9) ◽  
pp. 1111
Author(s):  
А.И. Мурзашев ◽  
А.П. Жуманазаров ◽  
М.Ю. Кокурин
Keyword(s):  
Experimental Data ◽  
Charge Transfer ◽  
Optical Absorption ◽  
Absorption Spectra ◽  
Coulomb Interaction ◽  
Energy Spectra ◽  
Optical Absorption Spectra ◽  
Endohedral Complexes

The article simulates the optical absorption spectra (OAS) of endohedral complexes Er2C2 @ C90 based on isomers No. 44 (C2) No. 21 (C1) of fullerene C90. For this purpose, the energy spectra of the indicated isomers have been calculated. The calculation was carried out within the framework of two models. Within the framework of the first model, which is traditional, only hops of π-electrons from site to site were taken into account (the integral of hopping to the nearest sites B ~ -2.6 eV). Within the framework of the second model, developed in a series of our works [1-5], in addition to hopping from site to site (the integral of hopping to the nearest sites B ~ -1.0 eV), the intrasite Coulomb interaction (ICCI) of π-electrons was also taken into account (the integral of the Coulomb interaction U ~ 7.0 eV). Comparison of the OSS curves obtained by us with the experimental data [5] convincingly indicates that the second model adequately describes the OSS of the endohedral Er2C2 @ C90 complexes based on the investigated isomers. The magnitude of charge transfer from the Er2C2 system to the fullerene shell turned out to be -4e.

scholarly journals Crystal-Field Mediated Electronic Transitions of EuS up to 35 GPa

2021 ◽  
Author(s):  
Virginia Monteseguro ◽  
Jose Antonio Barreda-Argüeso ◽  
Javier Ruiz-Fuertes ◽  
Angelika Rosa ◽  
Holger L. Meyerheim ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Crystal Field ◽  
Local Structure ◽  
Electronic Transitions ◽  
Metallic State ◽  
X Ray ◽  
Half Metal ◽  
Consistent Model ◽  
X Ray Absorption ◽  
Pressure Evolution

Abstract An advanced experimental and theoretical model to explain the correlation between the electronic and local structure of Eu2+ in two different environments within a same compound, EuS, is presented. EuX monochalcogenides (X: O, S, Se, Te) exhibit anomalies in all their properties around 14 GPa with a semiconductor to metal transition. Although it is known that these changes are related to the 4f75d0 → 4f65d1 electronic transition, no consistent model of the pressure-induced modifications of the electronic structure currently exists. We show, by optical and x-ray absorption spectroscopy, and by ab initio calculations up to 35 GPa, that the pressure evolution of the crystal field plays a major role in triggering the observed electronic transitions from semiconductor to the half-metal and finally to the metallic state.

X-ray diffuse scattering as precursor of incommensurate Peierls transitions in one-dimensional organic charge transfer conductors

2004 ◽  
Vol 219 (11) ◽  
Author(s):  
Jean-Paul Pouget
Keyword(s):  
Charge Transfer ◽  
Charge Density Wave ◽  
Diffuse Scattering ◽  
Lattice Distortion ◽  
Density Wave ◽  
Periodic Lattice ◽  
One Dimensional ◽  
X Ray ◽  
Charge Transfer Salts ◽  
A Charge

AbstractQuasi-one dimensional (1D) conductors of the TTF-TCNQ family of charge transfer salts exhibit a Peierls transition which stabilizes a periodic lattice distortion (PLD), accompanied by a charge density wave (CDW) modulation, with an incommensurate 2

Diffraction properties of a strongly bent diamond crystal used as a dispersive spectrometer for XFEL pulses

2019 ◽  
Vol 26 (4) ◽  
pp. 1069-1072 ◽  
Author(s):  
Liubov Samoylova ◽  
Ulrike Boesenberg ◽  
Aleksandr Chumakov ◽  
Vladimir Kaganer ◽  
Ilia Petrov ◽  
...  
Keyword(s):  
Experimental Data ◽  
Energy Spectrum ◽  
Strain Gradient ◽  
Free Electron ◽  
Diamond Crystal ◽  
Energy Spectra ◽  
Theoretical Modelling ◽  
Free Electron Lasers ◽  
X Ray ◽  
Stochastic Nature

Self-amplified spontaneous emission (SASE) enables X-ray free-electron lasers (XFELs) to generate hard X-ray pulses of sub-100 fs duration. However, due to the stochastic nature of SASE, the energy spectrum fluctuates from pulse to pulse. Many experiments that employ XFEL radiation require the resolution of the spectrum of each pulse. The work presented here investigates the capacity of a thin strongly bent diamond crystal to resolve the energy spectra of hard X-ray SASE pulses by studying its diffraction properties. Rocking curves of the symmetric C*(440) reflection have been measured for different bending radii. The experimental data match the theoretical modelling based on the Takagi–Taupin equations of dynamical diffraction. A uniform strain gradient has proven to be a valid model of strain deformations in the crystal.

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