Configuration-interaction-based time-dependent orbital approach for ab initio treatment of electronic dynamics in a strong optical laser field

The time-dependent configuration interaction singles (TDCIS) method-an ab initio electronic-structure technique with predictive character-is reformulated in terms of an effective one-electron theory with coupled channels. In this form, the TDCIS equations of motion may be evaluated using standard wave-packet propagation techniques in real space. The time-dependent orbital formulation of TDCIS has computational and conceptual advantages for studying strong-field phenomena in many-electron systems. A simplified version of this theory, referred to as the determinantal single-active-electron (d-SAE) method, is derived. TDCIS and d-SAE are tested by their application to a one-dimensional two-electron model in a strong laser field. The numerically exact time-dependent dipole moment of the interacting system is found to be very well reproduced with TDCIS. The d-SAE method is less accurate, but still provides superior performance in comparison to the standard single-active-electron approach.