Density-functional-theory investigation of antiproton-helium collisions

We revisit recent developments in the theoretical foundations of time-dependent density-functional theory TDDFT. TDDFT is then applied to the calculation of total cross sections for ionization processes in the p-He collision system. The Kohn-Sham potential is approximated as the sum of the Hartree-exchange potential and a correlation potential that was proposed in the context of laser-induced ionization. Furthermore, some approaches to the problem of calculating the ionization probabilities from the density are discussed. Small projectile energies 5 keV are considered as well as those in the range of 5 to 1000 keV. Results are compared to former calculations and to experimental data. We find that the correlation potential yields no obvious improvement of the results over the exchange-only approximation where the correlation potential is neglected. Furthermore, we find the problem of calculating the desired observables crucial, introducing errors of at least the same order of magnitude as the correlation potential. For the case of small energies, we find that trajectory effects play an important role: the ionization cross sections are enlarged significantly if curved instead of straight-line trajectories are used for the projectile motion.