Implementation of a gauge-invariant time-dependent configuration-interaction-singles method for three-dimensional atoms

Abstract

We present a numerical implementation of the gauge-invariant time-dependent configuration interaction singles (TDCIS) method [Appl. Sci. 8, 433 (2018)] for three-dimensional atoms. In our implementation, orbital-like quantity called channel orbital [Phys. Rev. A 74, 043420 (2006)] is propagated instead of configuration-interaction (CI) coefficients, which removes a computational bottleneck of explicitly calculating and storing numerous virtual orbitals. Furthermore, besides its physical consistency, the gauge-invariant formulation allows to take advantages of the velocity gauge treatment of the laser-electron interaction over the length gauge one in the simulation of high-field phenomena. We apply the present implementation to high-harmonic generation from helium and neon atoms, and numerically confirms the gauge invariance and demonstrates the effectiveness of the rotated velocity gauge treatment.

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

“…We have presented a successful evaluation of the amplitudes and phases of different photoionization paths from the TD-CASSCF simulation results for Ne irradiated by bichromatic XUV pulses. On one hand, the amplitude c m l of each partial wave is calculated as in equation (37) during the tSURFF procedure for ARPES and PAD calculation. The directly becomes the path amplitude c m ξ if the single path leads to (l, m).…”

“…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].…”

“…Again, we cannot resolve the paths 2p → s → p and 2p → d → p for m = 0 at this stage. In principle, one can further generalize equation (37) to relate both the partial wave amplitudes and phases to {g l,m p } and {D p q } (See Appendix A). Such an approach, however, cannot resolve multiple paths leading to the same partial wave (l, m).…”

“…In this appendix, we generalize equation (37) to relate both the partial wave amplitudes and phases to {g l,m p } and {D p q }. While the photoelectron is in general an ensemble (incoherent mixture) of different coherent wave packets, let us assume that {g l,m p } is obtained for one of them (e.g., each m for the linear polarization case).…”

Photoionization of aligned excited states in neon by attosecond laser pulses

“…This feature gives the MCTDHF method a flexibility that allows the use of a much smaller number of configurations than CI. In particular, we mention a set of methods which aim to take into account only the most relevant configurations, such as time-dependent completeactive-space self-consistent field (TD-CASSCF) [27], time-dependent configuration-interaction singles (TD-CIS) [28][29][30] and time-dependent restricted-active-space self-consistent field (TD-RASSCF) [31][32][33].…”