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Yoshinori Kitajima - One of the best experts on this subject based on the ideXlab platform.
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Observation of π backbonding features appearing in Fe 2p X-Ray Absorption Spectra and Fe 1s-4p-1s resonant X-Ray emission Spectra of RbMn[Fe(CN)6]
Journal of Physics: Conference Series, 2013Co-Authors: Yoshinori Kitajima, Yusuke Nanba, Masayuki Tanaka, Yuji Koga, Akihiro Ueno, Kosuke Nakagawa, Hiroko Tokoro, Shin-ichi Ohkoshi, Toshiaki Iwazumi, Kozo OkadaAbstract:Satellite features by p backbonding (metal-to-ligand charge transfer) were observed in both Fe 2p (L3,2-edge) X-Ray Absorption Spectra and 1s-4p-1s resonant X-Ray emission Spectra for RbMn[Fe(CN)6], which can be theoretically explained using common parameters. Fe L3,2-edge and Mn L3,2-edge X-Ray Absorption Spectra for low temperature phase are also presented.
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Comparison between X-Ray photoelectron and X-Ray Absorption Spectra of an environmental aerosol sample measured by synchrotron radiation
Spectrochimica Acta Part B: Atomic Spectroscopy, 1999Co-Authors: Jun Kawai, Tokujiro Yamamoto, Susumu Tohno, Yoshinori KitajimaAbstract:Abstract Sulfur X-Ray photoelectron Spectra (XPS) and X-Ray Absorption Spectra (XAS) of an aerosol sample collected by an Andersen sampler were measured using a synchrotron beam line. While the XPS was more surface sensitive than XAS, the detection limit of XAS was better than that of XPS. It was concluded that the XAS was more suitable for the chemical state analysis of sulfur in aerosol samples than XPS.
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K-edge X-Ray Absorption Spectra of argon in sputtered aluminum films
Spectrochimica Acta Part B: Atomic Spectroscopy, 1999Co-Authors: Momoko Takemura, Hideki Satake, Shigeru Yasuami, Masahiko Yoshiki, Yoshinori KitajimaAbstract:Abstract We have measured K–edge X–ray Absorption Spectra of argon in sputtered aluminum films at a synchrotron radiation facility (the Photon Factory). We found that the energy and shape of white line change when the film is annealed at 500 °C and the spectrum becomes resembling that of argon implanted in silicon. From the analyses of the X–ray Absorption Spectra and TEM observation we concluded that argon exists as very small atom clusters with a diameter less than 1 nm or exist as isolated atoms in the as–sputtered aluminum film, and that the size of the clusters become as big as 10 nm diameter when the film is heated.
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Grazing incidence X-Ray Absorption Spectra of (Si/W) 100/Si multilayer
Spectrochimica Acta Part B: Atomic Spectroscopy, 1999Co-Authors: Kouichi Hayashi, Yoshinori Kitajima, Hiroyuki Amano, Tokujiro Yamamoto, Jun Kawai, Hisataka TakenakaAbstract:Abstract Tungsten (W) M III X-Ray Absorption Spectra of a periodic multilayer, (Si/W) 100 /Si, were measured with the change of X-Ray grazing angle using sample current method. Under not total reflection condition, the absorbance changed little except at W M III Absorption edge. While under the total reflection condition, the absorbance increased with the increase of the X-Ray energy and the increment changed from low to high at the W M III Absorption edge. This result reflected the variation of the X-Ray evanescent wavelength caused by the Absorption effect of W.
Hans Ågren - One of the best experts on this subject based on the ideXlab platform.
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calculations of near edge x ray Absorption Spectra of gas phase and chemisorbed molecules by means of density functional and transition potential theory
Physical Review B, 1998Co-Authors: L Triguero, Lars G. M. Pettersson, Hans ÅgrenAbstract:We explore the utility of density-functional theory ~DFT! in conjunction with the transition-potential ~TP! method to simulate X-Ray-Absorption Spectra. Calculations on a set of small carbon-containing molecules and chemisorbed species show that this provides a viable option for obtaining excitation energies and oscillator strengths close to the experimental accuracy of core-valence transitions. Systematic variations in energy positions and intensities of the different Spectra in the test series have been investigated, and comparison is made with respect to the static exchange-, self-consistent-field, and explicit electron-correlation methods. The choice between standard exchange-correlation functionals is shown to be of little consequence for the valence resonant, here p*, parts of the X-Ray-Absorption Spectra, while the long-range behavior of presently available functionals is found not to be completely satisfactory for Rydberg-like transitions. Implementing a basis set augmentation technique, one finds that DFT methods still account well for most of the salient features in the near-edge X-Ray-Absorption Spectra, save for the multielectron transitions in the near continuum, and for some loss of Rydberg structure. For clusters modeling surface adsorbates, the DFT transition potential method reproduces well the Spectral compression and intensity reduction for the valence level Absorption compared to the free phase, provided fairly large clusters are taken into account. While for near-edge X-Ray-Absorption fine-structure ~NEXAFS! Spectra of free molecules the DFT-TP and Hartree-Fock/static exchange methods have complementary advantages, the DFT-TP method is clearly to be preferred when using clusters to simulate NEXAFS Spectra of surface adsorbates. @S0163-1829~98!00136-2#
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Assigning X-Ray Absorption Spectra by means of soft-X-Ray emission spectroscopy
Physical Review A, 1998Co-Authors: Kerstin M. Gunnelin, Peter Glans, P. Skytt, Jinghua Guo, Joseph Nordgren, Hans ÅgrenAbstract:The possibility to symmetry assign X-Ray Absorption Spectra using X-Ray emission spectroscopy is demonstrated. The oxygen K Spectra of CO2 are used to illustrate the possibility to assign core exci ...
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Static exchange and quantum defect analysis of X-Ray Absorption Spectra of carbonyl compounds
Physica Scripta, 1996Co-Authors: Li Yang, Hans Ågren, Vincenzo Carravetta, Lars G. M. PetterssonAbstract:We have performed quantum chemical calculations of carbon and oxygen X-Ray Absorption Spectra for a series of carbonyl containing molecules. Systematic variations in energy positions and intensities of the Spectra have been investigated. Based on the good reproduction of experimental Spectra, quantum defect and population analyses were utilized for detailed assignments. In some cases new assignments are proposed.
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Polarization features of X-Ray Absorption Spectra measured in the resonance inelastic X-Ray scattering mode
Physics Letters A, 1994Co-Authors: Faris Gel'mukhanov, Hans ÅgrenAbstract:Abstract Measurements of resonance inelastic X-Ray scattering photons can provide near edge X-Ray Absorption Spectra at ultra-high resolution. We derive the explicit polarization dependence for such measurements and show that it can be used as a crucial tool for symmetry assignments of bound core-excited states.
Ping Zhang - One of the best experts on this subject based on the ideXlab platform.
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First-Principles Calculation of Principal Hugoniot and K-Shell X-Ray Absorption Spectra for Warm Dense KCl
arXiv: Plasma Physics, 2015Co-Authors: Shijun Zhao, Shen Zhang, Wei Kang, Ping ZhangAbstract:Principal Hugoniot and K-shell X-Ray Absorption Spectra of warm dense KCl are calculated using the first-principles molecular dynamics method. Evolution of electronic structures as well as the influence of the approximate description of ionization on pressure (caused by the underestimation of the energy gap between conduction bands and valence bands) in the first-principles method are illustrated by the calculation. Pressure ionization and thermal smearing are shown as the major factors to prevent the deviation of pressure from global accumulation along the Hugoniot. In addition, cancellation between electronic kinetic pressure and virial pressure further reduces the deviation. The calculation of X-Ray Absorption Spectra shows that the band gap of KCl persists after the pressure ionization of the $3p$ electrons of Cl and K taking place at lower energy, which provides a detailed understanding to the evolution of electronic structures of warm dense matter.
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First-principles calculation of principal Hugoniot and K-shell X-Ray Absorption Spectra for warm dense KCl
Physics of Plasmas, 2015Co-Authors: Shijun Zhao, Shen Zhang, Wei Kang, Ping ZhangAbstract:Principal Hugoniot and K-shell X-Ray Absorption Spectra of warm dense KCl are calculated using the first-principles molecular dynamics (FPMD) method. Evolution of electronic structures as well as the influence of the approximate description of ionization on pressure (caused by the underestimation of the energy gap between conduction bands and valence bands) in the first-principles method are illustrated by the calculation. It is shown that approximate description of ionization in FPMD has small influence on Hugoniot pressure due to mutual compensation of electronic kinetic pressure and virial pressure. The calculation of X-Ray Absorption Spectra shows that the band gap of KCl persists after the pressure ionization of the 3p electrons of Cl and K taking place at lower energy, which provides a detailed understanding to the evolution of electronic structures of warm dense matter.
Shijun Zhao - One of the best experts on this subject based on the ideXlab platform.
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First-Principles Calculation of Principal Hugoniot and K-Shell X-Ray Absorption Spectra for Warm Dense KCl
arXiv: Plasma Physics, 2015Co-Authors: Shijun Zhao, Shen Zhang, Wei Kang, Ping ZhangAbstract:Principal Hugoniot and K-shell X-Ray Absorption Spectra of warm dense KCl are calculated using the first-principles molecular dynamics method. Evolution of electronic structures as well as the influence of the approximate description of ionization on pressure (caused by the underestimation of the energy gap between conduction bands and valence bands) in the first-principles method are illustrated by the calculation. Pressure ionization and thermal smearing are shown as the major factors to prevent the deviation of pressure from global accumulation along the Hugoniot. In addition, cancellation between electronic kinetic pressure and virial pressure further reduces the deviation. The calculation of X-Ray Absorption Spectra shows that the band gap of KCl persists after the pressure ionization of the $3p$ electrons of Cl and K taking place at lower energy, which provides a detailed understanding to the evolution of electronic structures of warm dense matter.
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First-principles calculation of principal Hugoniot and K-shell X-Ray Absorption Spectra for warm dense KCl
Physics of Plasmas, 2015Co-Authors: Shijun Zhao, Shen Zhang, Wei Kang, Ping ZhangAbstract:Principal Hugoniot and K-shell X-Ray Absorption Spectra of warm dense KCl are calculated using the first-principles molecular dynamics (FPMD) method. Evolution of electronic structures as well as the influence of the approximate description of ionization on pressure (caused by the underestimation of the energy gap between conduction bands and valence bands) in the first-principles method are illustrated by the calculation. It is shown that approximate description of ionization in FPMD has small influence on Hugoniot pressure due to mutual compensation of electronic kinetic pressure and virial pressure. The calculation of X-Ray Absorption Spectra shows that the band gap of KCl persists after the pressure ionization of the 3p electrons of Cl and K taking place at lower energy, which provides a detailed understanding to the evolution of electronic structures of warm dense matter.
John J. Rehr - One of the best experts on this subject based on the ideXlab platform.
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Automated generation and ensemble-learned matching of X-Ray Absorption Spectra
npj Computational Materials, 2018Co-Authors: Chen Zheng, John J. Rehr, Kiran Mathew, Chi Chen, Yiming Chen, Hanmei Tang, Alan Dozier, Fernando D. Vila, Louis F. J. Piper, Kristin A. PerssonAbstract:X-Ray Absorption spectroscopy (XAS) is a widely used materials characterization technique to determine oxidation states, coordination environment, and other local atomic structure information. Analysis of XAS relies on comparison of measured Spectra to reliable reference Spectra. However, existing databases of XAS Spectra are highly limited both in terms of the number of reference Spectra available as well as the breadth of chemistry coverage. In this work, we report the development of XASdb, a large database of computed reference XAS, and an Ensemble-Learned Spectra IdEntification (ELSIE) algorithm for the matching of Spectra. XASdb currently hosts more than 800,000 K-edge X-Ray Absorption near-edge Spectra (XANES) for over 40,000 materials from the open-science Materials Project database. We discuss a high-throughput automation framework for FEFF calculations, built on robust, rigorously benchmarked parameters. FEFF is a computer program uses a real-space Green’s function approach to calculate X-Ray Absorption Spectra. We will demonstrate that the ELSIE algorithm, which combines 33 weak “learners” comprising a set of preprocessing steps and a similarity metric, can achieve up to 84.2% accuracy in identifying the correct oxidation state and coordination environment of a test set of 19 K-edge XANES Spectra encompassing a diverse range of chemistries and crystal structures. The XASdb with the ELSIE algorithm has been integrated into a web application in the Materials Project, providing an important new public resource for the analysis of XAS to all materials researchers. Finally, the ELSIE algorithm itself has been made available as part of veidt , an open source machine-learning library for materials science. Analyzing X-Ray Absorption Spectra (XAS) just became easier thanks to a publically-available database and Spectra matching web tool. Interpreting XAS data is currently hindered by a lack of reference Spectra, which are laborious to obtain as they require finely tunable X-Rays only accessible at synchrotron facilities. Here, a collaboration led by Kristin Persson at the University of California Berkeley, and Shyu Ping Ong at the University of California San Diego developed a ‘high-throughput’ approach generating a large database of computed XAS data, along with a machine-learning algorithm matching unknown Spectra with ones in the database. The program correctly identified the oxidation states and coordination environments of a diverse test set of materials with high accuracy. The authors hope their web app will provide a valuable public resource for materials science researchers.
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Many-pole model of inelastic losses in X-Ray Absorption Spectra
Physical Review B, 2007Co-Authors: Joshua J. Kas, A. P. Sorini, Micah P. Prange, L. W. Cambell, J. A. Soininen, John J. RehrAbstract:Inelastic losses are crucial to a quantitative analysis of X-Ray Absorption Spectra. However, current treatments are semi-phenomenological in nature. Here a first-principles, many-pole generalization of the plasmon-pole model is developed for improved calculations of inelastic losses. The method is based on the GW approximation for the self-energy and real space multiple scattering calculations of the dielectric function for a given system. The model retains the efficiency of the plasmonpole model and is applicable both to periodic and aperiodic materials over a wide energy range. The same many-pole model is applied to extended GW calculations of the quasiparticle Spectral function. This yields estimates of multi-electron excitation effects, e.g., the many-body amplitude factor S 2 0 due to intrinsic losses. Illustrative calculations are compared with other GW calculations of the self-energy, the inelastic mean free path, and experimental X-Ray Absorption Spectra.
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Hole counts from X-Ray Absorption Spectra.
Journal of Synchrotron Radiation, 2001Co-Authors: A. L. Ankudinov, Alexey I. Nesvizhskii, John J. RehrAbstract:The interpretation of X-Ray Absorption Spectra in terms of electronic structure has long been of interest. Hole counts derived from such Spectra are often interpreted in terms of free-atom occupation numbers or Mulliken counts. It is shown here, however, that renormalized-atom (RA) and cellular counts are better choices to characterize the configuration of occupied electron states in molecules and condensed matter. A projection-operator approach is introduced to subtract delocalized states and to determine quantitatively such hole counts from X-Ray Absorption Spectra. The described approach is based on multiple-scattering theory (MST) and on atomic calculations of a smooth transformation relating the X-Ray Absorption Spectra to local projected densities of states (LDOS). Theoretical tests for the s and d electrons in transition metals show that the approach works well.
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Effect of Hydrogen Adsorption on the X-Ray Absorption Spectra of Small Pt Clusters
Physical review letters, 2001Co-Authors: A. L. Ankudinov, John J. Rehr, John J. Low, Simon R. BareAbstract:Hydrogen adsorption on Pt{sub 6}H{sub n} clusters leads to striking changes in the Pt L{sub 2,3} X-Ray Absorption Spectra. These effects are interpreted using a self-consistent real space Green's function approach. Calculations show that they are due largely to changes in the atomic background contribution to X-Ray Absorption (i.e., atomic X-Ray Absorption fine structure) and to reduced Pt-Pt scattering at the edge, while Pt-H multiple scattering is relatively weak. The origin of both effects is traced to the change in the local Pt potential due to Pt-H bonding.
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RELATIVISTIC CALCULATIONS OF SPIN-DEPENDENT X-Ray-Absorption Spectra
Physical Review B, 1997Co-Authors: A. L. Ankudinov, John J. RehrAbstract:An efficient interpolative approach is presented for relativistic calculations of polarized X-Ray-Absorption Spectra (XAS) including spin and spin-orbit interactions. The method is based on a spinor-relativistic Dirac-Fock treatment of atomic densities and dipole matrix elements, and a nonrelativistic treatment of propagation using high-order multiple scattering theory. This approach is implemented in an automated code FEFF7 which gives quantitative agreement with experiment for X-Ray magnetic circular dichroism of Gd and Fe, and for polarized XAS of Cd, including both scr(l){r_arrow}scr(l){plus_minus}1 dipole transitions. {copyright} {ital 1997} {ital The American Physical Society}
