Accurate Relativistic Real-Time Time-Dependent Density Functional Theory for Valence and Core Attosecond Transient Absorption Spectroscopy

TL;DR

This paper develops a relativistic real-time TDDFT framework, including a computationally efficient amfX2C approach, to accurately simulate attosecond transient absorption spectroscopy involving heavy elements and core excitations.

Contribution

It introduces a new relativistic RT-TDDFT methodology with the amfX2C Hamiltonian for efficient and accurate TAS simulations of heavy elements and core states.

Findings

amfX2C achieves accuracy comparable to 4c RT simulations

The method successfully models valence and core TAS processes

Provides physical insights into relativistic electron dynamics

Abstract

First principle theoretical modeling of out-of-equilibrium processes observed in attosecond pump-probe transient absorption spectroscopy (TAS) triggering pure electron dynamics remains a challenging task, specially for heavy elements and/or core excitations containing fingerprints of scalar and spin-orbit relativistic effects. To address this, we formulate a methodology for simulating TAS within the relativistic real-time time-dependent density functional theory (RT-TDDFT) framework, for both the valence and core energy regime. Especially for TAS, full four-component (4c) RT simulations are feasible but computationally demanding. Therefore, in addition to the 4c approach, we also introduce the atomic mean-field exact two-component (amfX2C) Hamiltonian accounting for one- and two-electron picture-change corrections within RT-TDDFT. amfX2C preserves the accuracy of the parent 4c method at a fraction of its computational cost. Finally, we apply the methodology to study valence and near L$_{2,3}$-edge TAS processes of experimentally relevant systems and provide additional physical insights using relativistic non-equilibrium response theory.