Application of the time-dependent surface flux method to the time-dependent multiconfiguration self-consistent-field method

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 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.

New Method for Measuring Angle-Resolved Phases in Photoemission

“…where χ k ðr; tÞ denotes the Volkov wave function and uðR s Þ the Heaviside function which is unity for r > R s and vanishes otherwise. The use of the Volkov wave function implies that we neglect the effects of the Coulomb force from the nucleus and the other electrons on the photoelectron dynamics outside R s , which is confirmed to be a good approximation [52]. The photoelectron momentum distribution ρðkÞ is given by…”

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

“…Our methods are gauge invariant; both length-gauge and velocitygauge simulations produce identical results for physical observables upon numerical convergence. The velocity gauge is known to be advantageous in simulating highfield phenomena 28,65,66 .…”

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

“…where χ k (r, t) denotes the Volkov wavefunction, and u(R s ) the Heaviside function which is unity for r > R s and vanishes otherwise. The use of the Volkov wavefunction implies that we neglect the effects of the Coulomb force from the nucleus and the other electrons on the photoelectron dynamics outside R s , which has been confirmed to be a good approximation [25]. The photoelectron momentum distribution ρ(k) is given by…”

“…From the obtained time-dependent wave functions, we extract the angle-resolved photoelectron energy spectrum (ARPES) by use of the time-dependent surface flux (tSURFF) method [24,25]. This method computes the ARPES from the electron flux through a surface located at a certain radius R s , beyond which the outgoing flux is absorbed by the infinite-range exterior complex scaling [22,23].…”

“…Not only the configuration-interaction coefficients {C I } but also orbitals are evolved in time, in order to describe excitation and ionization efficiently. We have developed variants of the TD-MCSCF methods called the time-dependent completeactive-space self-consistent field (TD-CASSCF) [17,21] and the time-dependent occupation-restricted multiple-active-space (TD-ORMAS) method [20], to which we have recently implemented infinite-range exterior complex scaling (irECS) [22,23] as an efficient absorbing boundary and the time-dependent surface flux (tSURFF) method [24,25] to calculate the angle-resolved photoelectron energy spectrum (ARPES). The excellent agreement with the experimental results of Ne photoionization by bichromatic FEL pulses [10] demonstrates high numerical accuracy of the methods.…”