Non-adiabatic quantum molecular dynamics: ionization of many-electron systems

We propose a novel method to describe realistically ionization processes with absorbing boundary conditions in basis expansion within the formalism of so-called non-adiabatic quantum molecular dynamics. This theory couples self-consistently a classical description of the nuclei with a quantum-mechanical treatment of the electrons in atomic many-body systems. In this paper, we extend the formalism by introducing absorbing boundary conditions via an imaginary potential. It is shown how this potential can be constructed in time-dependent density functional theory in basis expansion. The approach is first tested on the hydrogen atom and the pre-aligned hydrogen molecular ion H-2(+) in intense laser fields where reference calculations are available. It is then applied to study the ionization of non-aligned H-2(+) and H-2. Striking differences in the orientation dependence between both molecules are found. Surprisingly, enhanced ionization is predicted for perpendicularly aligned molecules.