Date(s) - Mar 2 2017
12:00 AM - 2:30 PM
Redwood Rooms C/D, Building 48
X-ray Spectroscopy Theory Lectures
John J. Rehr
Adjunct Professor of Photon Science, SLAC
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 . 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  and the introduction of vibrational damping with Debye-Waller factors  yield significant improvements. Additional losses such as multi-electron excitations can be treated using cumulant-expansion techniques and the quasi-boson approximation . 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 .
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