AUTHOR=Pathak Himadri , Sato Takeshi , Ishikawa Kenichi L. 

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

JOURNAL=Frontiers in Chemistry

VOLUME=10

YEAR=2022

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2022.982120

DOI=10.3389/fchem.2022.982120

ISSN=2296-2646

ABSTRACT=<p>We report the formulation of a new, cost-effective approximation method in the time-dependent optimized coupled-cluster (TD-OCC) framework [T. Sato <italic>et al.</italic>, 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 <italic>O</italic>(<italic>N</italic><sup>7</sup>) with respect to the number of active orbitals <italic>N</italic>. 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.</p>