Time-dependent restricted active space Configuration Interaction for the photoionization of many-electron atoms

TL;DR

This paper presents a versatile time-dependent restricted active space CI method for accurately modeling photoionization in many-electron atoms, unifying various approximation schemes and demonstrating its effectiveness on helium and beryllium.

Contribution

The paper introduces a general time-dependent RAS-CI approach that unifies multiple existing methods for simulating atomic photoionization processes.

Findings

Accurate photoionization cross sections for Helium and Beryllium

Successful modeling of X-ray--IR pump-probe ionization in Beryllium

Method's versatility in incorporating various approximation schemes

Abstract

We introduce the time-dependent restricted active space Configuration Interaction method to solve the time-dependent Schr\"odinger equation for many-electron atoms, and particularly apply it to the treatment of photoionization processes in atoms. The method is presented in a very general formulation and incorporates a wide range of commonly used approximation schemes, like the single-active electron approximation, time-dependent Configuration Interaction with single-excitations, or the time-dependent R-matrix method. We proof the applicability of the method by calculating the photoionization cross sections of Helium and Beryllium, as well as the X-ray--IR pump-probe ionization in Beryllium