Simulation of attosecond transient soft X-ray absorption in solids using generalized Kohn-Sham real-time TDDFT

Abstract

Time-dependent density functional theory (TDDFT) simulations of transient core-level spectroscopies require a balanced treatment of both valenceand core-electron excitations.To this end, tuned range-separated hybrid exchange-correlation functionals within the generalized Kohn-Sham scheme offer a computationally efficient means of simultaneously improving the accuracy of valence and core excitation energies in TDDFT by mitigating delocalization errors across multiple length-scales. In this work range-separated hybrid functionals are employed in conjunction with the velocity-gauge formulation of real-time TDDFT to simulate static as well as transient soft X-ray near-edge absorption spectra in a prototypical solid-state system, monolayer hexagonal boron nitride, where excitonic effects are important. In the static case, computed soft X-ray absorption edge energies and line shapes are seen to be in good agreement with experiment. Following laser excitation by a pump pulse, soft X-ray probe spectra are shown to exhibit characteristic features of population induced bleaching and transient energy shifts of exciton peaks. The methods outlined in this work therefore illustrate a practical means for simulating attosecond timeresolved core-level spectra in solids within a TDDFT framework.

Intruder Peak-Free Transient Inner-Shell Spectra Using Real-Time Simulations

“…These modulations are complicated, and reversing from time-delay to actual time typically requires first-principles simulations of both the dynamics and the observed spectra. 28,29 There are numerous first-principles methods for simulating X-ray near edge spectra for the linear response (unpumped) case. Correlated methods for XANES include the following: algebraic diagrammatic construction (ADC), 30−32 equation-ofmotion coupled-cluster (EOM-CC), 33−36 Bethe-Salpeter equation with GW approximation, 37,38 etc.…”