Correct dissociation behavior of radical ions such as H2+ in density functional calculations

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