The Multi-Configurational Hartree-Fock close-coupling ansatz: application to Argon photoionization cross section and delays

TL;DR

This paper introduces a robust ab initio multi-configurational Hartree-Fock close-coupling method combined with exterior complex scaling to accurately compute argon photoionization cross sections and delays, validated against experimental data.

Contribution

It develops a novel computational approach integrating multi-configurational Hartree-Fock and complex scaling for precise photoionization analysis.

Findings

Validated method on argon resonances

Accurate energy-dependent photoionization delays

Agreement with experimental measurements

Abstract

We present a robust, ab initio method for addressing atom-light interactions and apply it to photoionization of argon. We use a close-coupling ansatz constructed on a multi-configurational Hartree-Fock description of localized states and B-spline expansions of the electron radial wave functions. In this implementation, the general many-electron problem can be tackled thanks to the use of the ATSP2K libraries [CPC 176 (2007) 559]. In the present contribution, we combine this method with exterior complex scaling, thereby allowing for the computation of the complex partial amplitudes that encode the whole dynamics of the photoionization process. The method is validated on the 3s3p6np series of resonances converging to the 3s extraction. Then, it is used for computing the energy dependent differential atomic delay between 3p and 3s photoemission, and agreement is found with the measurements of Gu\'enot et al. [PRA 85 (2012) 053424]. The effect of the presence of resonances in the one-photon spectrum on photoionization delay measurements is studied.