Correlation in time-dependent density-functional-theory studies of antiproton-helium collisions

Correlation effects are examined in the context of time-dependent density-functional-theory calculations of antiproton-helium collisions. An approximation for the correlation potential as well as two models for the correlation integral are explored. The first of these makes use of frozen correlation, while the second is appropriated from the world of laser-induced ionization. Total cross sections for both single and double ionization in the impact energy range 5-2000 keV are presented. While the results of the first model provide little improvement over an independent electron model description the second model agrees quite well with experimental results for both single and double ionization. Our results also lend credence to the belief that an appropriate approximation of the correlation integral is more important in reproducing correlation effects than the correlation potential.