  We extend to strongly correlated molecular systems the recently introduced
basis-set incompleteness correction based on density-functional theory (DFT)
[E. Giner et al., J. Chem. Phys. 149, 194301 (2018)]. This basis-set correction
relies on a mapping between wave-function calculations in a finite basis set
and range-separated DFT (RSDFT) through the definition of an effective
non-divergent interaction corresponding to the electron-electron Coulomb
interaction projected in the finite basis set. This enables the use of
RSDFT-type complementary density functionals to recover the dominant part of
the short-range correlation effects missing in this finite basis set. To study
both weak and strong correlation regimes we consider the potential energy
curves of the H10, N2, O2, and F2 molecules up to the dissociation limit, and
we explore various approximations of complementary functionals fulfilling two
key properties: spin-multiplet degeneracy (i.e., independence of the energy
with respect to the spin projection Sz) and size consistency. Specifically, we
investigate the dependence of the functional on different types of on-top pair
densities and spin polarizations. The key result of this study is that the
explicit dependence on the on-top pair density allows one to completely remove
the dependence on any form of spin polarization without any significant loss of
accuracy. Quantitatively, we show that the basis-set correction reaches
chemical accuracy on atomization energies with triple-zeta quality basis sets
for most of the systems studied here. Also, the present basis-set
incompleteness correction provides smooth potential energy curves along the
whole range of internuclear distances.
