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A Review on Ab Initio Approaches for Multielectron Dynamics

In parallel with the evolution of femtosecond and attosecond laser as well as free-electron laser technology, a variety of theoretical methods have been developed to describe the behavior of atoms, molecules, clusters, and solids under the action of those laser pulses. Here we review major ab initio wave-function-based numerical approaches to simulate multielectron dynamics in atoms and molecules driven by intense long-wavelength and/or ultrashort short-wavelength laser pulses. Direct solution of the time-dependent Schrödinger equation (TDSE), though its applicability is limited to He, ${\rm H}_2$, and Li, can provide an exact description and has been greatly contributing to the understanding of dynamical electron-electron correlation. Multiconfiguration self-consistent-field (MCSCF) approach offers a flexible framework from which a variety of methods can be derived to treat both atoms and molecules, with possibility to systematically control the accuracy. The equations of motion of configuration interaction coefficients and molecular orbitals for general MCSCF ansatz have recently been derived. Time-dependent extension of the $R$-matrix theory, originally develop for electron-atom collision, can realistically and accurately describe laser-driven complex multielectron atoms.