Time-dependent many-electron treatment of electronic energy and charge transfer in atomic collisions

Electronic energy and charge transfer in atomic collisions are described within a first principles molecular dynamics including an explicit treatment of electronic motions, in terms of time-dependent many-electron wavefunctions. Following an overview of treatments in the literature based on expansions in sets of adiabatic and diabatic electronic states, this article emphazises the use of time-dependent molecular orbitals and time-dependent Hartree-Fock states. Three fundamental problems are identified in a first principles dynamics, relating to the calculation of state-to-state transition probabilities and expectation values, to the translational motion of electrons moving with nuclei, and to the coupling of fast electronic transitions and slow nuclear motions. Solutions to these problems are described on the basis of an eikonal representation of wavefunctions and sums over initial conditions, of the use of traveling atomic functions to expand molecular orbitals, and of a relax-and-drive propagation procedure for electrons and nuclei. Examples are presented of applications in ion-atom and ion-surface collisions, relating to electronic excitation and charge transfer, orbital polarization, and light emission during collisions.