  A two-electron one-dimensional model of a heteroatomic molecule composed of
two open-shell atoms is considered. Including only two electrons isolates and
examines the effect that the highest occupied molecular orbital has on the
Kohn-Sham potential as the molecule dissociates. We reproduce the
characteristic step and peak that previous high-level wavefunction methods have
shown to exist for real molecules in the low-density internuclear region. The
simplicity of our model enables us to investigate in detail their development
as a function of bond-length, with little computational effort, and derive
properties of their features in the dissociation limit. We show that the onset
of the step is coincident with the internuclear separation at which an avoided
crossing between the ground-state and lowest charge-transfer excited state is
approached. Although the step and peak features have little effect on the
ground-state energetics, we discuss their important consequences for dynamics
and response.
