**Date/Time**

Date(s) - Mar 2 2017

*12:00 AM - 2:30 PM*

**Location**

Redwood Rooms C/D, Building 48

**Category(ies)**

**X-ray Spectroscopy Theory Lectures**

**John J. Rehr**

Adjunct Professor of Photon Science, SLAC

and

Dept of Physics, University of Washington

III Inelastic losses and Many-body effects

IV Real-time approaches

The first two parts of this series covered: I) Introduction to X-ray Spectroscopy Theory, and II Real-space Green’s function Theory and FEFF. Now we aim to cover some more advanced aspects of the theory. Lecture III is devoted to many-body effects which are essential to quantitative investigations of XAS. Recent advances now permit parameter-free calculations of the key effects [1]. Physically, they arise from electronic correlations and atomic vibrations that lead to inelastic losses and damping. Quasi-particle (QP) approaches with a GW self-energy such as the GW/Bethe-Salpeter equation [2] and the introduction of vibrational damping with Debye-Waller factors [3] yield significant improvements. Additional losses such as multi-electron excitations can be treated using cumulant-expansion techniques and the quasi-boson approximation [4]. Next, Lecture IV) describes real-time approaches, which are becoming increasingly important in photon spectroscopies ranging from linear and non-linear optical response to XAS with pulsed sources. Here we discuss methods based on real-time, time-dependent density functional theory (RT-TDDFT) and time-correlation functions. Finally we discuss a real-time approach for calculations of dynamic structure in nano-scale materials base on finite-temperature density functional theory based molecular dynamics and the real-space Green’s function approach in FEFF9. This approach is illustrated for the case of supported Pt nanoclusters [5].

[1] John J. Rehr et al., Comptes Rendus Physique **10**, 548 (2009).

[2] K. Gilmore et al., Comput. Phys. Comm. **197**, 109 (2015).

[3] F. Vila et al., Phys. Rev. B 78, 121404(R), (2008).

[3] Jianqiang Sky Zhou et al., J. Chem. Phys. **143**, 194109 (2015).

[4] Y. Takimoto et al., J. Rehr, J. Chem. Phys. 127, 154114 (2007).

[5] A.I. Frenkel et al., J. Vac. Sci. Technol. A 32, 020801 (2014).