Advanced calculations of X-ray spectroscopies with <i>FEFF10</i> and Corvus

Kas, J. J.; Vila, Fernando D.; Pemmaraju, C. D.; Tan, Tun S.; Rehr, J. J.

doi:10.1107/s1600577521008614

Cited by 47 publications

(39 citation statements)

References 51 publications

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“…Vibrational effects are included in terms of a correlated Debye model for the fine-structure at low T in XAS or a configurational average for XANES at high T . The FT generalization introduced here is implemented as an extension of the FEFF codes in a new version FEFF10 [12]. The approach has been tested against various experiments, and typically yields good quantitative agreement.…”

Section: Discussionmentioning

confidence: 99%

“…As at T = 0, the approach is based on the one-particle electron Green's function, which is calculated either by matrix inversion or by a well converged multiple-scattering path expansion. Our current implementation builds upon the theory and algorithms used in the FEFF9 code [9], and has been incorporated in a new version FEFF10 [12]. This theory is illustrated here with a number of examples.…”

Section: Introductionmentioning

confidence: 99%

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Real-space Green's function approach for x-ray spectra at high temperature

2021

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There has been considerable interest in properties of condensed matter at finite temperature, including non-equilibrium behavior and extreme conditions up to the warm dense matter regime. Such behavior is encountered, e.g., in experimental time-resolved x-ray absorption spectroscopy (XAS) in the presence of intense laser fields. In an effort to simulate such behavior, we present an approach for calculations of finite-temperature x-ray absorption spectra in arbitrary materials, using a generalization of the real-space Green's function formalism. The method is incorporated as an option in the core-level x-ray spectroscopy code FEFF10. To illustrate the approach, we present calculations for several materials together with comparisons to experiment and with other methods.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Real-space Green's function approach for x-ray spectra at high temperature

2021

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“…In this case, it is more appropriate to compute S nl (q, E) with ab initio calculations. We use the FEFF [31,32] code, which performs a full quantum mechanical treatment to sum over all transition probabilities from the initial state to all possible atomic final states in the target material. FEFF was primarily developed (and has been extensively validated) for X-ray absorption spectroscopy [33] but includes the option to calculate a S nl (q, E) for non-resonant inelastic X-ray scattering (NRIXS) [34] 1 .…”

Section: Compton Scatteringmentioning

confidence: 99%

Precision measurement of Compton scattering in silicon with a skipper CCD for dark matter detection

Norcini,

Castello-Mor,

Baxter

et al. 2022

Preprint

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Experiments aiming to directly detect dark matter through particle recoils can achieve energy thresholds of O(10 eV). In this regime, ionization signals from small-angle Compton scatters of environmental γ-rays constitute a significant background. Monte Carlo simulations used to build background models have not been experimentally validated at these low energies. We report a precision measurement of Compton scattering on silicon atomic shell electrons down to 23 eV. A skipper charge-coupled device (CCD) with single-electron resolution, developed for the DAMIC-M experiment, was exposed to a 241 Am γ-ray source over several months. Features associated with the silicon K, L1, and L2,3-shells are clearly identified, and scattering on valence electrons is detected for the first time below 100 eV. We find that the relativistic impulse approximation for Compton scattering, which is implemented in Monte Carlo simulations commonly used by direct detection experiments, does not reproduce the measured spectrum below 0.5 keV. The data are in better agreement with ab initio calculations originally developed for X-ray absorption spectroscopy.

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“…Calculations of the imaginary part of Σ GW (k, ω, T ) involves a singe integral over the magnitude of q but to obtained the real part we need to perform a Kramers-Kronig transform resulting in a double integral. In typical RSGF XAS calculations [46], tens of thousands of selfenergy evaluations are required. Thus that calculation of quasiparticle self-energy Σ GW (k, k 2 /2, T ) immediately becomes a computational bottleneck.…”

Section: Theory Summary a Finite-temperature X-ray Absorptionmentioning

confidence: 99%

High-temperature self-energy corrections to x-ray absorption spectra

Tan¹,

Kas²,

Trickey³

et al. 2022

Preprint

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Effects of finite-temperature quasiparticle self-energy corrections to x-ray absorption spectra are investigated within the finite-temperature quasiparticle local density GW approximation up to temperatures T of order the Fermi temperature. To facilitate the calculations, we parametrize the quasiparticle self-energy using low-order polynomial fits. We show that temperature-driven decrease in the electron lifetime substantially broadens the spectra in the near-edge region with increasing T . However, the quasiparticle shift is most strongly modified near the onset of plasmon excitations.

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Advanced calculations of X-ray spectroscopies with FEFF10 and Corvus

Cited by 47 publications

References 51 publications

Real-space Green's function approach for x-ray spectra at high temperature

Real-space Green's function approach for x-ray spectra at high temperature

Precision measurement of Compton scattering in silicon with a skipper CCD for dark matter detection

High-temperature self-energy corrections to x-ray absorption spectra

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