Low-energy collisions of electrons with highly polar molecules: Orthogonalization and model exchange potentials

The importance of imposing orthogonality constraints on the continuum wave functions calculated from model exchange potentials for electron collisions with the highly polar systems LiH and LiF is demonstrated. The $\Sigma$ and $\Pi$ resonance features in $e$-LiF collisions, found in earlier model-exchange calculations, disappear upon imposing orthogonality; no evidence for these features is observed in the exact static-exchange calculations.