Abstract
We present a numerical implementation of the time-dependent surface flux (tSURFF) method [New J. Phys. 14, 013021 (2012)], an efficient computational scheme to extract photoelectron energy spectra, to the time-dependent multiconfiguration self-consistent-field (TD-MCSCF) method. Extending the original tSURFF method developed for single particle systems, we formulate the equations of motion for the spectral amplitude of orbital functions constutiting the TD-MCSCF wave function, from which the angle-resolved photoelectron energy spectrum, and more generally, photoelectron reduced density matrices (RDMs) are readiliy obtained. The tSURFF method applied to the TD-MCSCF wave function, in combination with an efficient absorbing boundary offered by the infinite-range exterior complex scaling, enables accurate {\it ab initio} computations of photoelectron energy spectra from multielectron systems subject to an intense and ultrashort laser pulse with a computational cost significantly reduced compared to that required in projecting the total wave function onto scattering states. We apply the present implementation to the photoionization of Ne exposed to an attosecond extreme-ultraviolet (XUV) pulse and above-threshold ionization of Ar irradiated by an intense mid-infrared laser field, demonstrating both accuracy and efficiency of the present method.
Highlights
The rapid progress in experimental techniques for highintensity, ultrashort optical pulses has led to the advent and development of strong-field physics and attosecond science [1,2], with the ultimate goal to directly measure and control electron motion in atoms, molecules, and solids
We have presented a successful numerical implementation of time-dependent surface flux (tSURFF) to the TD-MCSCF (TD-CASSCF and TDORMAS) methods to extract angle-resolved photoelectron energy spectra from laser-driven multielectron atoms
To obtain Photoelectron energy spectra (PES) in systems described within the MCSCF framework, the photoelectron reduced density matrix has been introduced, whose diagonal elements in the momentum space correspond to PES
Summary
The rapid progress in experimental techniques for highintensity, ultrashort optical pulses has led to the advent and development of strong-field physics and attosecond science [1,2], with the ultimate goal to directly measure and control electron motion in atoms, molecules, and solids. Configurations for a given number of orbitals as in the multiconfiguration time-dependent Hartree-Fock (MCTDHF) method [4,5,6], the computational cost increases factorially with the number of electrons. To overcome this difficulty, we have recently formulated and numerically implemented the time-dependent complete-active-space self-consistentfield (TD-CASSCF) method [9], and even more general and less demanding time-dependent occupation-restricted multiple-active-space (TD-ORMAS) method [12]. Under a physically reasonable assumption that the nuclear potential and interelectronic Coulomb interaction are negligible for photoelectron dynamics in the region distant from the nuclei, we derive the equations of motion for the momentum amplitudes of each orbital They contain an additional term compared with the single-electron case.
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