scholarly journals Relativistic Corrections to Phase Shift Calculation in the GNXAS Package

Symmetry ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 1021
Author(s):  
Nodoka Hara ◽  
Andrea Di Di Cicco ◽  
Georghii Tchoudinov ◽  
Keisuke Hatada ◽  
Calogero Renzo Natoli
Keyword(s):  
Phase Shift ◽  
Multiple Scattering ◽  
Cross Sections ◽  
Basic Structure ◽  
Absorption Cross ◽  
Structural Refinement ◽  
Relativistic Case ◽  
X Ray ◽  
Relativistic Corrections ◽  
X Ray Absorption

Modern XAFS (X-ray Absorption Fine Structure) data-analysis is based on accurate multiple-scattering (MS) calculations of the x-ray absorption cross-section. In this paper, we present the inclusion and test of relativistic corrections for the multiple-scattering calculations within the GnXAS suite of programs, which is relevant to the treatment of the XAFS signals when atoms with high atomic number are contained into the system. We present a suitable strategy for introducing relativistic corrections without altering the basic structure of the programs. In particular, this is realized by modifying only the Phagen program calculating the atomic absorption cross sections and scattering t-matrices for the selected cluster. The modification incorporates a pseudo-Schrödinger Equation (SE) replacing the Dirac relativistic form. The phase-shift calculations have been put to a test in two known molecular and crystalline cases: molecular bromine Br2 and crystalline Pb. Calculations in an extended energy range have been shown to be very close to the non-relativistic case for Br2 (Br K-edge) while corrections have been found to exceed 25% for amplitude and phases of the XAFS multiple-scattering signals (Pb L3-edge). Benefits in the structural refinement using relativistic corrections are discussed for crystalline Pb at room temperature.

scholarly journals Fullerite C60 optical constants in the C 1s NEXAFS region

2021 ◽  
Vol 2103 (1) ◽  
pp. 012168
Author(s):  
D V Sivkov ◽  
S V Nekipelov ◽  
O V Petrova ◽  
D V Bogachuk ◽  
R N Skandakov ◽  
...  
Keyword(s):  
Cross Sections ◽  
Optical Constants ◽  
Absorption Cross ◽  
X Ray ◽  
Carbon Absorption ◽  
Cross Section Spectrum ◽  
Integral Relations ◽  
Atomic Form Factor ◽  
Using Data ◽  
X Ray Absorption

Abstract Using data on the absorption cross sections the refraction coefficient spectral dependence n(E) and the spectra of the remaining optical coefficients (reflection coefficient, phase shift, and atomic form factor) in the fullerite C60 C 1s near edge X-ray absorption fine structure (NEXAFS) region (280–350 eV) were determined. For the n(E) calculations the Kramers-Kronig integral relations (KKRs) were used. The KKR computations were performed using data on atomic carbon absorption cross sections in the 10–30000 eV range and on solid and gaseous C60 – in the 0–120 eV. Absorption cross section spectrum in the fullerite C60 C 1s NEXAFS region were measured.

scholarly journals Cr L-Edge X-ray Absorption Spectroscopy of CrIII(acac)3 in Solution with Measured and Calculated Absolute Absorption Cross Sections

2018 ◽  
Vol 122 (29) ◽  
pp. 7375-7384 ◽  
Author(s):  
Markus Kubin ◽  
Meiyuan Guo ◽  
Maria Ekimova ◽  
Erik Källman ◽  
Jan Kern ◽  
...  
Keyword(s):  
Absorption Spectroscopy ◽  
Cross Sections ◽  
Absorption Cross ◽  
X Ray ◽  
X Ray Absorption

Multiple Scattering Calculations Applied to XAS: A Structure and Electronic Sensitive Tool

1991 ◽  
Vol 253 ◽  
Author(s):  
Philippe Sainctavit ◽  
J. Petiau
Keyword(s):  
Multiple Scattering ◽  
Cross Section ◽  
Absorption Cross Section ◽  
Scattering Theory ◽  
Spectral Features ◽  
Absorption Cross ◽  
Multiple Scattering Theory ◽  
X Ray ◽  
Sensitive Tool ◽  
X Ray Absorption

ABSTRACTWe present an application of multiple scattering theory with “muffin-tin” potentials to the calculation of X-ray absorption cross section. We have measured and calculated the K-edge spectra of atoms in compounds with zincblende structure : SiC, ZnS. We show that some spectral features can be precisely related to the local environnement around the absorbing atom.

Photoelectric Atomic Absorption Cross Sections for Elements 2 = 6 to 54 in the Medium Energy X-ray Range 5 to 25 keY

1975 ◽  
Vol 30 (9) ◽  
pp. 1133-1142 ◽  
Author(s):  
J. D. Stephenson
Keyword(s):  
Atomic Absorption ◽  
Cross Sections ◽  
Absorption Cross ◽  
Medium Energy ◽  
Absorption Coefficients ◽  
X Ray ◽  
Rigorous Theory ◽  
Mass Absorption ◽  
X Ray Absorption

A comparison is made between recent computations of X-ray photoeffect absorption cross sections, using screened hydrogen-like eigenfunctions, given in Part I1, and those of an alternate more rigorous theory together with those estimable from experimental X-ray absorption coefficients. Some inherent limitations, which restrict the present results, are discussed. Photoeffect mass absorption coefficients for a limited number of elements between Z = 10 and 39 are determined from the hydrogen-like theory, using five characteristic X-ray energies from NiLa 1 (0.852 keV) to TiLa 1 (4.511 keV)

SIGMAL: A Program for Calculating L-Shell lonization Cross-Sections

1981 ◽  
Vol 39 ◽  
pp. 198-199 ◽  
Author(s):  
R.F. Egerton
Keyword(s):  
Cross Sections ◽  
Fortran Program ◽  
Absorption Data ◽  
X Ray ◽  
Atomic Electrons ◽  
Energy Dependent ◽  
Hydrogenic Model ◽  
Electron Energy Loss ◽  
X Ray Absorption ◽  
Shell Ionization

SIGMAL is a short (∼ 100-line) Fortran program designed to rapidly compute cross-sections for L-shell ionization, particularly the partial crosssections required in quantitative electron energy-loss microanalysis. The program is based on a hydrogenic model, the L1 and L23 subshells being represented by scaled Coulombic wave functions, which allows the generalized oscillator strength (GOS) to be expressed analytically. In this basic form, the model predicts too large a cross-section at energies near to the ionization edge (see Fig. 1), due mainly to the fact that the screening effect of the atomic electrons is assumed constant over the L-shell region. This can be remedied by applying an energy-dependent correction to the GOS or to the effective nuclear charge, resulting in much closer agreement with experimental X-ray absorption data and with more sophisticated calculations (see Fig. 1 ).

Extended X-ray absorption fine structure and multiple-scattering simulation of nickel dithiolene complexes Ni[S2C2(CF3)2]2n(n= −2, −1, 0) and an olefin adduct Ni[S2C2(CF3)2]2(1-hexene)

2015 ◽  
Vol 22 (1) ◽  
pp. 124-129 ◽  
Author(s):  
Weiwei Gu ◽  
Hongxin Wang ◽  
Kun Wang
Keyword(s):  
Fine Structure ◽  
Multiple Scattering ◽  
Edge Structure ◽  
X Ray ◽  
Absorption Fine ◽  
Square Planar ◽  
Square Planar Complexes ◽  
Uv Visible ◽  
Edge Features ◽  
X Ray Absorption

A series of Ni dithiolene complexes Ni[S2C2(CF3)]2n(n= −2, −1, 0) (1,2,3) and a 1-hexene adduct Ni[S2C2(CF3)2]2(C6H12) (4) have been examined by NiK-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectroscopies. Ni XANES for1–3reveals clear pre-edge features and approximately +0.7 eV shift in the NiK-edge position for `one-electron' oxidation. EXAFS simulation shows that the Ni—S bond distances for1,2and3(2.11–2.16 Å) are within the typical values for square planar complexes and decrease by ∼0.022 Å for each `one-electron' oxidation. The changes in NiK-edge energy positions and Ni—S distances are consistent with the `non-innocent' character of the dithiolene ligand. The Ni—C interactions at ∼3.0 Å are analyzed and the multiple-scattering parameters are also determined, leading to a better simulation for the overall EXAFS spectra. The 1-hexene adduct4presents no pre-edge feature, and its NiK-edge position shifts by −0.8 eV in comparison with its starting dithiolene complex3. Consistently, EXAFS also showed that the Ni—S distances in4elongate by ∼0.046 Å in comparison with3. The evidence confirms that the neutral complex is `reduced' upon addition of olefin, presumably by olefin donating the π-electron density to the LUMO of3as suggested by UV/visible spectroscopy in the literature.

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