John Rehr (TIMES Lecture)

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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).