Simulating weak-field attosecond processes with a Lanczos reduced basis approach to time-dependent equation-of-motion coupled-cluster theory

Abstract

A time-dependent equation-of-motion coupled-cluster singles and doubles (TD-EOM-CCSD) method is implemented, which uses a reduced basis calculated with the asymmetric band Lanczos algorithm. The approach is used to study weak-field processes in small molecules induced by ultrashort valence pump and core probe pulses. We assess the reliability of the procedure by comparing TD-EOM-CCSD absorption spectra to spectra obtained from the time-dependent coupled-cluster singles and doubles method, and observe that spectral features can be reproduced for several molecules, at much lower computational times. We discuss how multiphoton absorption and symmetry can be handled in the method, and general features of the core-valence separation projection technique. We also model the transient absorption of an attosecond x-ray probe pulse by the glycine molecule.

Linear and Nonlinear Optical Properties from TDOMP2 Theory

“…While TDCC theory propagates the well-known exponential Ansätze for the wave functions, TD-EOM-CC theory expresses them as the linear combinations of EOM-CC left and right eigenstates. While both approaches are expected to give similar results (and, indeed, appear to do so, see ref ( 33 )) for weak-field processes, only the TDCC theory (albeit with dynamical orbitals) has been successfully applied to strong-field phenomena such as ionization dynamics and high harmonic generation 20 to date.…”

“… 10 − 12 Avoiding the factorial computational scaling caused by the full configuration interaction (FCI) treatment at the heart of these approaches, time-dependent extensions of single-reference coupled-cluster (CC) theory 13 and equation-of-motion CC (EOM-CC) theory 14 , 15 have been increasingly often used to simulate laser-driven many-electron dynamics in the time domain in recent years. 16 − 33 The two approaches, time-dependent CC (TDCC) and time-dependent EOM-CC (TD-EOM-CC) theories, differ in their parametrization of the time-dependent left and right wave functions. While TDCC theory propagates the well-known exponential Ansätze for the wave functions, TD-EOM-CC theory expresses them as the linear combinations of EOM-CC left and right eigenstates.…”

“…It is no surprise, therefore, that the most widely used RT electronic structure method is RT time-dependent density-functional theory (RT-TDDFT). − Highly accurate wave function-based RT methods have also been developed, including multiconfigurational time-dependent Hartree–Fock (MCTDHF) − theory and related complete, restricted, and generalized active space formulations. − Avoiding the factorial computational scaling caused by the full configuration interaction (FCI) treatment at the heart of these approaches, time-dependent extensions of single-reference coupled-cluster (CC) theory and equation-of-motion CC (EOM-CC) theory , have been increasingly often used to simulate laser-driven many-electron dynamics in the time domain in recent years. − The two approaches, time-dependent CC (TDCC) and time-dependent EOM-CC (TD-EOM-CC) theories, differ in their parametrization of the time-dependent left and right wave functions. While TDCC theory propagates the well-known exponential Ansätze for the wave functions, TD-EOM-CC theory expresses them as the linear combinations of EOM-CC left and right eigenstates.…”

Comparing real-time coupled cluster methods through simulation of collective Rabi oscillations

“…where O A (t) and O B (t) are subsystem operators. Equation (24) then implies that the similarity transformed operator in Eq. ( 18) can be written as the tensor sum…”

“…Variants of the time-dependent equation-of-motion coupled cluster (TD-EOM-CC) method have also been used for modeling laser-molecule interactions, but only a handful applications have included the full non-linear real-time propagation of the laser-driven electron dynamics [13,[22][23][24]. In these cases, the TD-EOM-CC equations were expressed in the basis obtained by diagonalizing the field-free equation-of-motion coupled cluster Hamiltonian.…”