  Using the formalism of the conditional amplitude, we study the response part
of the exchange-correlation potential in the strong-coupling limit of density
functional theory, analysing its peculiar features and comparing it with the
response potential averaged over the coupling constant for small atoms and for
the hydrogen molecule. We also use a simple one-dimensional model of a
stretched heteronuclear molecule to derive exact properties of the response
potential in the strong-coupling limit. The simplicity of the model allows us
to unveil relevant features also of the exact Kohn-Sham potential and its
different components, namely the appearance of a second peak in the correlation
kinetic potential on the side of the most electronegative atom.
