Density functional theory investigation of antiproton-helium collisions

TL;DR

This paper applies time-dependent density functional theory to calculate ionization cross sections in antiproton-helium collisions, comparing different approximations and trajectory models, and analyzing the accuracy of the methods against experimental data.

Contribution

It demonstrates the application of TDDFT to collision problems and evaluates the impact of correlation potentials and trajectory effects on ionization cross section calculations.

Findings

Correlation potential does not improve results over exchange-only approximation.

Errors in calculating observables are significant, comparable to correlation effects.

Trajectory curvature significantly increases ionization cross sections at low energies.

Abstract

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 antiproton-Helium 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 below 5keV are considered as well as those in the range from 5 to 1000 keV. Results are compared with former calculations and with 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.