Transient X-ray absorption spectra in solids from generalized Kohn-Sham real-time TDDFT.

Simulating transient X-ray absorption spectra in solids with TDDFT requires at a minimum, a balanced treatment of both localized core and possibly delocalized valence excitations. To this end range-separated hybrid exchange-correlation functionals offer improved accuracy by mitigating self-interaction errors across multiple length-scales [1,2]. In this work the velocity-gauge formulation of real-time TDDFT is combined with multiply-range-separated hybrid functionals to simulate transient soft X-ray near-edge absorption spectra in solids where excitonic effects are important. Immediately following laser excitation by few femtosecond pump pulses, soft X-ray probe spectra are shown to exhibit characteristic features of population induced bleaching and transient energy shifts of exciton peaks. Simulation results are assessed for accuracy by comparison with experimental data on prototypical solid state systems.
[1] Imamura et al, Chemical Physics Letters 618 (2015) 30–36
[2] C. D. Pemmaraju, Computational Condensed Matter 18, e00348 (2019)