Time-dependent optimized coupled-cluster method with doubles and perturbative triples [TD-OCCD(T)] for first principles simulation of multielectron dynamics

TL;DR

This paper introduces TD-OCCD(T), a new, efficient, and accurate time-dependent coupled-cluster method with doubles and perturbative triples for simulating multielectron dynamics under intense laser fields, improving computational feasibility.

Contribution

The paper develops TD-OCCD(T), a novel orbital-optimized, size-extensive, gauge-invariant method extending CCSD(T) to time-dependent multielectron dynamics, with scalable equations of motion.

Findings

Demonstrated effectiveness in simulating strong-field ionization of Kr atom.

Compared favorably with TD-CASSCF, TD-OCCDT, and TDHF methods.

Scales as O(N^7) with active orbitals.

Abstract

We report the formulation of a new, cost-effective approximation method in the time-dependent optimized coupled-cluster (TD-OCC) framework [T. Sato et al., J. Chem. Phys. 148, 051101 (2018)] for first-principles simulations of multielectron dynamics in an intense laser field. The method, designated as TD-OCCD(T), is a time-dependent, orbital-optimized extension of the "gold-standard" CCSD(T) method in the ground-state electronic structure theory. The equations of motion for the orbital functions and the coupled-cluster amplitudes are derived based on the real-valued time-dependent variational principle using the fourth-order Lagrangian. The TD-OCCD(T) is size extensive and gauge invariant, and scales as O(N^7) with respect to the number of active orbitals N. The pilot application of the TD-OCCD(T) method to the strong-field ionization and high-order harmonic generation from a Kr atom is reported in comparison with the results of the previously developed methods, such as the time-dependent complete-active-space self-consistent field (TD-CASSCF), TD-OCC with double and triple excitations (TD-OCCDT), TD-OCC with double excitations (TD-OCCD), and the time-dependent Hartree-Fock (TDHF) methods.