  We find the numerically exact partition potential for 1-D systems of
interacting electrons designed to model diatomic molecules. At integer fragment
occupations, the kinetic contribution to the partition potential develops sharp
features in the internuclear region that nearly cancel corresponding features
of exchange-correlation. They occur at locations that coincide with those of
well-known features of the underlying molecular Kohn-Sham potential. For
non-integer fragment occupations, we demonstrate that the fragment Kohn-Sham
gaps determine the kinetic part of the partition potential. Our results
highlight the importance of non-additive noninteracting kinetic and
exchange-correlation energy approximations in density-embedding methods at
large internuclear separations and the importance of non-additive
noninteracting kinetic energy approximations at all separations.
