Momentum distributions in time-dependent density functional theory: Product phase approximation for non-sequential double ionization in strong laser fields

摘要

We investigate the possibility to deduce momentum space properties fromtime-dependent density functional calculations. Electron and ion momentumdistributions after double ionization of a model Helium atom in a strongfew-cycle laser pulse are studied. We show that, in this case, the choice ofsuitable functionals for the observables is considerably more important thanthe choice of the correlation potential in the time-dependent Kohn-Shamequations. By comparison with the solution of the time-dependent Schroedingerequation, the insufficiency of functionals neglecting electron correlation isdemonstrated. We construct a functional of the Kohn-Sham orbitals, which inprinciple yields the exact momentum distributions of the electrons and the ion.The product-phase approximation is introduced, which reduces the problem ofapproximating this functional significantly.