Time-dependent complete-active-space self-consistent-field method for atoms: Application to high-harmonic generation

TL;DR

This paper introduces a comprehensive numerical implementation of the time-dependent complete-active-space self-consistent-field (TD-CASSCF) method for atoms under strong laser fields, enabling detailed analysis of electron dynamics and high-harmonic generation.

Contribution

The paper presents a full-dimensional, gauge-invariant TD-CASSCF implementation with efficient Coulomb mean field evaluation and stable propagation techniques for atomic systems.

Findings

Successful application to high-harmonic generation in helium, beryllium, and neon.

Demonstrates the importance of electron correlations in high-harmonic generation.

Provides a stable and scalable computational framework for strong-field atomic physics.

Abstract

We present the numerical implementation of the time-dependent complete-active-space self-consistent-field (TD-CASSCF) method [Phys. Rev. A, 88, 023402 (2013)] for atoms driven by a strong linearly polarized laser pulse. The present implementation treats the problem in its full dimensionality and introduces a gauge-invariant frozen-core approximation, an efficient evaluation of the Coulomb mean field scaling linearly with the number of basis functions, and a split-operator method specifically designed for stable propagation of stiff spatial derivative operators. We apply this method to high-harmonic generation in helium, beryllium, and neon and explore the role of electron correlations.