Long-range charge-transfer excitations pose a major challenge for
time-dependent density functional approximations. We show that
spin-symmetry-breaking offers a simple solution for molecules composed of
open-shell fragments, yielding accurate excitations at large separations when
the acceptor effectively contains one active electron. Unrestricted
exact-exchange and self-interaction-corrected functionals are performed on
one-dimensional models and the real LiH molecule within the pseudopotential
approximation to demonstrate our results.Comment: 5 pages, 4 figure
