  Proper treatment of charge delocalization, besides nondynamic correlation,
has been a major challenge to density functional theory. Contemporary
functionals are known to undershoot the dissociation of symmetric charged dimer
A2+, a simple but stringent test, and predict a spurious barrier and improperly
delocalize charges for charged molecular clusters. We extend a functional
designed to treat nondynamic correlation to treat also the charge
delocalization with a modification of the secondary nondynamic correlation for
parallel spins. The modified functional is shown to eliminate those problems
and reduces the multi-electron self-interaction error. Furthermore, its results
are the closest to that of CCSD(T) in the whole range of the dissociation
compared with contemporary functionals. It also correctly localizes the net
positive charge in (CH4)n+ clusters and predicts a nearly constant ionization
potential as result. Overall, we show the feasibility of treating charge
delocalization together with nondynamic correlation.
