A combined R-matrix eigenstate basis set and finite-differences propagation method for the time-dependent Schr\"{od}dinger equation: the one-electron case

TL;DR

This paper introduces a novel combined R-matrix basis set and finite-differences propagation method for solving the time-dependent Schrödinger equation in atomic systems, enabling efficient treatment of multi-region problems under strong fields.

Contribution

It presents the first combined basis set and grid approach for multi-region TDSE problems, specifically tailored for single active electron systems in intense laser fields.

Findings

Successfully applied to hydrogen atom in intense laser field

Demonstrates accurate wavefunction propagation across regions

Validates the method's effectiveness for single-electron dynamics

Abstract

In this work we present the theoretical framework for the solution of the time-dependent Schr\"{o}dinger equation (TDSE) of atomic and molecular systems under strong electromagnetic fields with the configuration space of the electron's coordinates separated over two regions, that is regions $I$ and $II$. In region $I$ the solution of the TDSE is obtained by an R-matrix basis set representation of the time-dependent wavefunction. In region $II$ a grid representation of the wavefunction is considered and propagation in space and time is obtained through the finite-differences method. It appears this is the first time a combination of basis set and grid methods has been put forward for tackling multi-region time-dependent problems. In both regions, a high-order explicit scheme is employed for the time propagation. While, in a purely hydrogenic system no approximation is involved due to this separation, in multi-electron systems the validity and the usefulness of the present method relies on the basic assumption of R-matrix theory, namely that beyond a certain distance (encompassing region $I$) a single ejected electron is distinguishable from the other electrons of the multi-electron system and evolves there (region II) effectively as a one-electron system. The method is developed in detail for single active electron systems and applied to the exemplar case of the hydrogen atom in an intense laser field.