Study of laser-driven multielectron dynamics of Ne atom using time-dependent optimised second-order many-body perturbation theory

Abstract

We calculate the high-harmonic generation (HHG) spectra, strong-field ionisation, and timedependent dipole-moment of Ne using explicitly time-dependent optimised second-order manybody perturbation method (TD-OMP2) where both orbitals and amplitudes are time-dependent. We consider near-infrared (800 nm) and mid-infrared (1200 nm) laser pulses with very high intensities (5 × 10 14 , 8 × 10 14 , and 1 × 10 15 W/cm 2), required for strong-field experiments with the high-ionisation potential (21.6 eV) atom. We compare the result of the TD-OMP2 method with the time-dependent complete-active-space self-consistent field method and the time-dependent Hartree-Fock method. Further, we report the implementation of the TD-CC2 method within the chosen active space, which is also a second-order approximation to the TD-CCSD method, and present results of time-dependent dipole-moment and HHG spectra with an intensity of 5 × 10 13 W/cm 2 at a wavelength of 800 nm. It is found that the TD-CC2 method is not stable in the case with a higher laser intensity, and it does not provide a gauge-invariant description of the physical properties, which makes TD-OMP2 a superior choice to reach out to larger chemical systems, especially for the study of strong-field dynamics. The obtained results indicate that the TD-OMP2 method shows moderate performance, overestimating the response of Ne, while TDHF underestimates it..

Interferometric extraction of photoionization-path amplitudes and phases from time-dependent multiconfiguration self-consistent-field simulations

“…The negligibly small standard errors and consistent values for the two simulation runs for ω = 15.9 eV (labels A and B) indicate successful fitting, which is also evident from the quasi-perfect agreement between the TD-CASSCF outputs and the reproduction from equations ( 40)-( 45) using the obtained amplitudes and phases in Fig. 1 and Table 5 40), (42), and (44) using the amplitudes and phases obtained through the global fitting procedure described in the text (lines). The TD-CASSCF calculations were done at eight values of φ between 0 and 7 4 π with an interval of π 4 .…”

“…While we have presented the results for Ne with the TD-CASSCF methods, we can also treat other atomic systems. Moreover, it will be straightforward to apply the present method in combination with various real-time ab initio approaches such as different types of TD-MCSCF methods with moving orbitals [12,13,14,15,16,17,18,19], the time-dependent configuration-interaction method [34,35,36,37], the time-dependent optimized coupled cluster method [38,39,40,41,42], and the time-dependent density functional theory [43,44,45].…”

Time-dependent optimized coupled-cluster method for multielectron dynamics IV: Approximate consideration of the triple excitation amplitudes

“…57. We have also reported the implementation and numerical assessments of the second-order approximation to the time-dependent coupled-cluster single double (TD-CCSD) method, called the TD-CC2 method 58 . The stationary variant of this method (CC2) 59 is one of the widely accepted lower-cost methods.…”

“…It is closely related to the stationary CCSDT1 method of Bartlett and coworkers 60,61 . We do not include single excitation amplitudes following our previous work 38,[56][57][58] but optimize the orbitals according to TDVP, which is ideally suited for studying strong-field dynamics involving substantial excitation and ionization. The TD-OCCDT(4) method inherits gauge invariance from the parent TD-OCCDT method due to the variational optimization of orbitals.…”

Interpretation of Coupled-Cluster Many-Electron Dynamics in Terms of Stationary States

“…Yielding energies, structures, and properties with excellent accuracy for both ground-and excited states of weakly correlated systems, it has become one of the most trusted methods of molecular quantum chemistry. 15 Recent years have witnessed increasing interest in time-dependent CC (TDCC) theory [16][17][18][19][20] for numerical simulations of many-body quantum dynamics in nuclear, 21 and atomic and molecular [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] systems. In addition, TDCC theory plays a key role in recent work on finite-temperature CC theory for molecular 39,40 and extended 41 systems.…”