Das Pemmaraj (Special Seminar)

Date(s) - Apr 20 2016
11:00 AM - 12:00 PM

SLAC Building 137, Room 322


Interpretation of ultrafast time-resolved core-level spectroscopies using excited-state density functional approaches

Das Pemmaraju
The Molecular Foundry and Chemical Sciences Division,
Lawrence Berkeley National Laboratory, Berkeley, CA-94720

The availability of ultrashort pulses in the X-ray and extreme ultraviolet (XUV) ranges from powerful free electron laser light-sources and table top high-harmonic generation respectively, has significantly enhanced the utility of core-level excitations as probes for investigating dynamical processes in materials on femto- to atto-second timescales. Theoretical approaches to complement increasingly popular ultrafast core-level spectroscopies are therefore actively being developed. In this context, I will discuss the utility of beyond-ground-state density functional methods such as constrained density functional theory (c-DFT) and time-dependent density functional theory (TDDFT) in the interpretation of time-resolved spectroscopies, with the help of two illustrative case studies: In the first, a combination of c-DFT and TDDFT is used to interpret transient core-level shifts induced by photoexcited dynamics in a femtosecond time-resolved xray photoelectron spectroscopy study of a N3 dye molecule chemisorbed onto a ZnO substrate [1]. In the second, non- equilibrium electron-hole densities obtained from real-time TDDFT simulations of the valence electronic structure [2, 3] are employed to estimate the modulation of the L-edge absorption in femtosecond laser-excited silicon as observed using attosecond XUV probe pulses [4]. An analysis of these simulations can provide valuable insights into the nature of the underlying electron dynamics as well as inform our continued efforts to improve and extend the scope of such theory efforts.

[1] Siefermann et al, J. Phys. Chem. Lett., 5, 2753 (2014)
[2] Yabana et al, Phys. Rev. B 85, 045134 (2012)
[3] Dutoi et al, Phys. Rev. A 88, 013419 (2013)
[4] Schultze et al., Science, 346, 1348 (2014)