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

TL;DR

This paper demonstrates a computational approach using generalized Kohn-Sham real-time TDDFT with range-separated hybrid functionals to simulate attosecond transient soft X-ray absorption spectra in solids, accurately capturing excitonic effects and transient phenomena.

Contribution

It introduces a practical method combining range-separated hybrid functionals with real-time TDDFT to simulate transient core-level spectra in solids, improving accuracy for valence and core excitations.

Findings

Computed static soft X-ray absorption spectra agree with experiments.

Simulated transient spectra show bleaching and energy shifts of exciton peaks.

Method effectively captures ultrafast dynamics in solid-state systems.

Abstract

Time-dependent density functional theory (TDDFT) simulations of transient core-level spectroscopies require a balanced treatment of both valence- and 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 time-resolved core-level spectra in solids within a TDDFT framework.