  We perform model calculations for a stretched LiF molecule, demonstrating
that nonadiabatic charge transfer effects can be accurately and seamlessly
described within a density functional framework. In alkali halides like LiF,
there is an abrupt change in the ground state electronic distribution due to an
electron transfer at a critical bond length $R=R_c$, where a barely avoided
crossing of the lowest adiabatic potential energy surfaces calls the validity
of the Born-Oppenheimer approximation into doubt. Modeling the $R$-dependent
electronic structure of LiF within a two-site Hubbard model, we find that
nonadiabatic electron-nuclear coupling produces a sizable elongation of the
critical $R_c$ by 0.5 Bohr. This effect is very accurately captured by a simple
and rigorously-derived correction, with an $M^{-1}$ prefactor, to the
exchange-correlation potential in density functional theory; $M=$ reduced
nuclear mass. Since this nonadiabatic term depends on gradients of the nuclear
wavefunction and conditional electronic density, $\nabla_R \chi(R)$ and
$\nabla_R n(\mathbf{r},R)$, it couples the Kohn-Sham equations at neighboring
$R$ points. Motivated by an observed localization of nonadiabatic effects in
nuclear configuration space, we propose a local conditional density
approximation -- an approximation that reduces the search for nonadiabatic
density functionals to the search for a single function $y(n)$.
