Time-dependent restricted-active-space self-consistent-field singles method for many-electron dynamics

TL;DR

The paper introduces the TD-RASSCF-S method, a hybrid approach for simulating many-electron dynamics in atoms and molecules, combining features of MCTDHF and TDCIS, and demonstrating improved accuracy and efficiency.

Contribution

The paper develops the TD-RASSCF-S method, which achieves full convergence with fewer orbitals and surpasses TDCIS accuracy, enabling large-system simulations.

Findings

TD-RASSCF-S wave function converges with N_e/2+1 to N_e orbitals.

The method outperforms TDCIS in high-order harmonic generation spectra.

Applicable to large systems beyond MCTDHF capabilities.

Abstract

The time-dependent restricted-active-space self-consistent-field singles (TD-RASSCF-S) method is presented for investigating TD many-electron dynamics in atoms and molecules. Adopting the SCF notion from the muticonfigurational TD Hartree-Fock (MCTDHF) method and the RAS scheme (single-orbital excitation concept) from the TD configuration-interaction singles (TDCIS) method, the TD-RASSCF-S method can be regarded as a hybrid of them. We prove that, for closed-shell $N_{\rm e}$-electron systems, the TD-RASSCF-S wave function can be fully converged using only $N_{\rm e}/2+1\le M\le N_{\rm e}$ spatial orbitals. Importantly, based on the TD variational principle, the converged TD-RASSCF-S wave function with $M= N_{\rm e}$ is more accurate than the TDCIS wave function. The accuracy of the TD-RASSCF-S approach over the TDCIS is illustrated by the calculation of high-order harmonic generation spectra for one-dimensional models of atomic helium, beryllium, and carbon in an intense laser pulse. The electronic dynamics during the process is investigated by analyzing the behavior of electron density and orbitals. The TD-RASSCF-S method is accurate, numerically tractable, and applicable for large systems beyond the capability of the MCTDHF method.