Study Of Laser-Driven Multielectron Dynamics Of Ne Atom Using Time-Dependent Optimised Second-Order Many-Body Perturbation Theory

We calculate the high-harmonic generation (HHG) spectra, strong-field ionisation, and time-dependent 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 x 10(14), 8 x 10(14), and 1 x 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 x 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.[GRAPHICS].