X-Ray Spectroscopy

The x-ray spectroscopy (XRS) aims to develop theoretical techniques for quantitative calculations of the various core-level spectroscopies measured at modern x-ray synchrotron facilities. These include x-ray absorption spectra (XAS), i.e., x-ray absorption fine structure (XAFS) and x-ray absorption near edge structure (XANES), and related spectra such as x-ray magnetic circular dichroism (XMCD), which are widely used to understand structural, vibrational and magnetic properties ofmaterials.

The primary engine for these calculations is the FEFF code. This approach uses a Real-space Green's function (RSGF) approach that builds in many-body effects such as inelastic losses, core-hole screening, and Debye-Waller factors [1,2] . Additional many body effects are treated with TDDFT, BSE, and spectral functions [2] . The RSGF approach in FEFF can also calculate core-level x-ray scattering factors (including diffraction anomalous spectra), x-ray emission spectra (XES), non-resonant X-ray Raman scattering (XRS) and core-level electron energy loss spectra (EELS) and various optical constants from the UV-x-ray energies. The approach is generally applicable to aperiodic systems throughout the periodic table, including bulk, surfaces, nano-structures, liquids, biostructures and other disordered materials as illustrated, e.g., in [3,4].

[1] J. J. Rehr and R. C. Albers, Rev. Mod. Phys. 72, 621 (2000).
[2] John J. Rehr et al., Comptes Rendus de Physique 10, 548 (2009).
[3] John J. Rehr et al., Phys. Chem. Chem. Phys. 1 2, 5503 (2010).
[4] Veronesi et al., Phys. Rev. B 82, 0201 01 (2010).

What do we calculate?

• Core level X-ray absorption spectra (XAS): X-ray absorption fine structure (XAFS), X-ray absorption near edge structure (XANES), and X-ray magnetic circular dichroism (XMCD).
• X-ray scattering factors, X-ray emission spectra, non-resonant X-ray Raman scattering (XRS) and electron energy loss spectra (EELS).

Which systems do we study?

• Bulk, Surfaces and Nanostructures. Liquids.

Methodology

• Real-space Green's function (RSGF) approaches including quasi-particle effects (GW), core-hole screening, and Debye-Waller factors.
• Additional many body effects treated with TDDFT, BSE, and spectral functions.

How to use ETSF services?

• Introduction Package for New Users.

Beamline Coordinator

Prof. John Rehr

University of Washington, Seattle, USA
jjr [at] phys [dot] washington [dot] edu

References

• Theoretical approaches to x-ray absorption fine structure ,
  J. J. Rehr and R. C. Albers, Rev. Mod. Phys. 72, 621 (2000).
• Theory and calculations of X-ray spectra: XAS, XES, XRS, and NRIXS ,
  J.J. Rehr, Radiation Physics and Chemistry 75, 1547 (2006).
• FEFF Project.