Correct dissociation behavior of radical ions such as H-2(+) in density functional calculations

In this contribution it is shown that the unphysical dissociation energy cu rves of dimeric ions bearing a small odd number of electrons as obtained wi th DFT calculations can be cured by a posteriori corrections. The self-inte raction error, which is known to be at the origin of the unphysical dissoci ation behavior, is corrected by a Slater's transition state calculation. A very satisfactory dissociation energy curve is obtained for He-2(+). Howeve r for H-2(+) it is also necessary to introduce fractional occupation number s to obtain a good description of the system. (C) 2001 American Institute o f Physics.