  The charge delocalization error, besides nondynamic correlation, has been a
major challenge to density functional theory. Contemporary functionals
undershoot the dissociation of symmetric charged dimers A2+, a simple but
stringent test, predict a spurious barrier and improperly delocalize charges
for charged molecular clusters. We extend a functional designed for nondynamic
correlation to treat the charge delocalization error by modifying the
nondynamic correlation for parallel spins. The modified functional eliminates
those problems and reduces the multielectron self-interaction error.
Furthermore, its results are the closest to those of CCSD(T) in the whole range
of the dissociation compared with contemporary functionals. It correctly
localizes the net positive charge in (CH4)n+ clusters and predicts a nearly
constant ionization potential as a result. Testing of the SIE4x4 set shows that
the new functional outperforms a wide variety of functionals assessed for this
set in the literature. Overall, we show the feasibility of treating charge
delocalization together with nondynamic correlation.
