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)2076-341710.3390/app8030433] for three-dimensional atoms. In our implementation, an orbital-like quantity called a channel orbital [Phys. Rev. A 74, 043420 (2006)PLRAAN1050-294710.1103/PhysRevA.74.043420] 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 us to take advantage 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-order harmonic generation from helium and neon atoms, which numerically confirms the gauge invariance and demonstrates the effectiveness of the rotated velocity gauge treatment.