Self-Adaptive Real-Time Time-Dependent Density Functional Theory for X-ray Absorptions

TL;DR

This paper introduces AutoPST, an automatic method to optimize the propagator, step size, and simulation time in real-time TDDFT calculations for X-ray absorption spectra, enhancing efficiency and accuracy.

Contribution

The paper presents AutoPST, a novel automated approach for selecting optimal parameters in relativistic RT-TDDFT simulations of XAS, improving computational efficiency.

Findings

AutoPST effectively determines optimal simulation parameters.

Enhanced accuracy in XAS simulations with reduced computational cost.

Applicable to relativistic RT-TDDFT calculations.

Abstract

Real-time time-dependent density functional theory (RT-TDDFT) can in principle access the whole absorption spectrum of a many-electron system exposed to a narrow pulse. However, this requires an accurate and efficient propagator for the numerical integration of the time-dependent Kohn-Sham equation. While a low-order time propagator is already sufficient for the low-lying valence absorption spectra, it is no longer the case for the X-ray absorption spectra (XAS) of systems composed even only of light elements, for which the use of a high-order propagator is indispensable. It is then crucial to choose a largest possible time step and a shortest possible simulation time, so as to minimize the computational cost. To this end, we propose here a robust AutoPST approach to determine automatically (Auto) the propagator (P), step (S), and time (T) for relativistic RT-TDDFT simulations of XAS.