Time-dependent optimized coupled-cluster method with doubles and perturbative triples for first principles simulation of multielectron dynamics

Himadri Pathak; Takeshi Sato; Kenichi L Ishikawa

doi:10.3389/fchem.2022.982120

Time-dependent optimized coupled-cluster method with doubles and perturbative triples for first principles simulation of multielectron dynamics

Front Chem. 2022 Sep 13:10:982120. doi: 10.3389/fchem.2022.982120. eCollection 2022.

Authors

Himadri Pathak¹, Takeshi Sato^{1

2

3}, Kenichi L Ishikawa^{1

2

3}

Affiliations

¹ Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, Tokyo, Japan.
² Photon Science Center, School of Engineering, The University of Tokyo, Tokyo, Japan.
³ Research Institute for Photon Science and Laser Technology, The University of Tokyo, Tokyo, Japan.

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.

Keywords: high harmonic generation; multielectron dynamics; strong field ionization; strong laser field; time-dependent optimized coupled-cluster.