*Map Unavailable*

**Date/Time**

Date(s) - Jul 15 2019

*11:00 AM - 12:30 PM*

**Location**

Sycamore Room, Building 40, room 195

**Category(ies)**

**John J. Rehr**

**Adjunct Professor of Photon Science, SLAC**

and

**Dept. of Physics, University of Washington**

**Seattle, WA 98195-1560**

** I Introduction to X-ray Spectroscopy Theory**

**II Real-space Green’s function Theory and FEFF**

There has been dramatic progress both in calculations and the interpretation of x-ray and electron spectroscopies, ranging from x-ray absorption spectra (XAS) and inelastic x-ray scattering (IXS) to electron energy loss spectra (EELS). Using modern synchrotron radiation x-ray sources, these spectroscopies have become powerful probes of complex materials ranging from catalysts and minerals to bio-structures and aqueous solutions. Combined with modern theory, these spectroscopies now permit an interpretation in terms of the structural, electronic, magnetic and vibrational properties of a system. This Lecture series aims to summarize these theoretical developments.

Lecture I presents an introduction to x-ray spectroscopy theory, starting with a qualitative, phenomenological discussion of both x-ray absorption fine structure (XAFS) and near-edge structure (XANES). We then present an overview of various quantitative approaches using approximations ranging from density functional theory and quantum chemistry methods to quasi-particle methods and the Bethe-Salpeter equation.

Lecture II is devoted to a more detailed treatment of the multiple-scattering approach used in the x-ray spectroscopy and excited state electronic structure codes FEFF [1,2]. This approach is based on real-space Green’s function techniques, rather than wave-functions and other approximations that considerably speed up calculations for systems throughout the periodic table. The approach used in FEFF also builds in key many-body effects and relativistic corrections.

Subsequent lectures will treat the theory at a more advanced level: Lecture III covers many-body effects and inelastic losses, and Lecture IV real-time approaches.

[1] J. J. Rehr, J. J. Kas, M. P. Prange, A. P. Sorini, Y. Takimoto, F. Vila,

Comptes Rendus Physique **10**, 548 (2009).

[2] J. J. Rehr and R. C. Albers, Rev. Mod. Phys. **72**, 621 (2000).