Time-dependent complete-active-space self-consistent field method for multielectron dynamics in intense laser fields

TL;DR

The paper introduces a time-dependent complete-active-space self-consistent-field (TD-CASSCF) method for accurately simulating multielectron dynamics in intense laser fields, enabling detailed studies of ultrafast phenomena in atoms and molecules.

Contribution

It presents a flexible, accurate TD-CASSCF approach that includes a classification of orbital subspaces and encompasses MCTDHF as a special case, advancing multielectron dynamics simulations.

Findings

TD-CASSCF closely reproduces MCTDHF results with sufficient active orbitals.

The method effectively models ionization dynamics in LiH and LiH dimer.

It enables first-principles studies of ultrafast phenomena in complex systems.

Abstract

The time-dependent complete-active-space self-consistent-field (TD-CASSCF) method for the description of multielectron dynamics in intense laser fields is presented, and a comprehensive description of the method is given. It introduces the concept of frozen-core (to model tightly bound electrons with no response to the field), dynamical-core (to model electrons tightly bound but responding to the field), and active (fully correlated to describe ionizing electrons) orbital subspaces, allowing compact yet accurate representation of ionization dynamics in many-electron systems. The classification into the subspaces can be done flexibly, according to simulated physical situations and desired accuracy, and the multiconfiguration time-dependent Hartree-Fock (MCTDHF) approach is included as a special case. To assess its performance, we apply the TD-CASSCF method to the ionization dynamics of one-dimensional lithium hydride (LiH) and LiH dimer models, and confirm that the present method closely reproduces rigorous MCTDHF results if active orbital space is chosen large enough to include appreciably ionizing electrons. The TD-CASSCF method will open a way to the first-principle theoretical study of intense-field induced ultrafast phenomena in realistic atoms and molecules.