Implementation of infinite-range exterior complex scaling to the time-dependent complete-active-space self-consistent-field method

TL;DR

This paper introduces an efficient implementation of infinite-range exterior complex scaling (irECS) within the time-dependent complete-active-space self-consistent-field (TD-CASSCF) method, significantly improving simulation accuracy and reducing computational costs for multielectron atoms under intense laser pulses.

Contribution

The paper develops a novel irECS implementation using Gauss-Laguerre-Radau quadrature in TD-CASSCF, enabling accurate, cost-effective simulations of strong-field phenomena in multielectron atoms.

Findings

Achieves up to 80% reduction in computational cost for high-harmonic generation simulations.

Effectively prevents unphysical wave packet reflections at the boundary.

Enables accurate simulations of double ionization processes.

Abstract

We present a numerical implementation of the infinite-range exterior complex scaling (irECS) [Phys. Rev. A 81, 053845 (2010)] as an efficient absorbing boundary to the time-dependent complete-active-space self-consistent field (TD-CASSCF) method [Phys. Rev. A 94, 023405 (2016)] for multielectron atoms subject to an intense laser pulse. We introduce Gauss-Laguerre-Radau quadrature points to construct discrete variable representation basis functions in the last radial finite element extending to infinity. This implementation is applied to strong-field ionization and high-harmonic generation in He, Be, and Ne atoms. It efficiently prevents unphysical reflection of photoelectron wave packets at the simulation boundary, enabling accurate simulations with substantially reduced computational cost, even under significant (~ 50%) double ionization. For the case of a simulation of high-harmonic generation from Ne, for example, 80% cost reduction is achieved, compared to a mask-function absorption boundary.