We find the numerically exact embedding potential of Partition-DFT (P-DFT) for 1-D systems of interacting electrons designed to model diatomic molecules. A defining feature of P-DFT is the ensemble treatment of electrons in fragments. At integer fragment occupations, the kinetic contribution to the embedding 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 energy gaps determine the kinetic part of the embedding potential. Our results highlight the importance of non-additive non-interacting kinetic and exchange-correlation energy approximations in density-embedding methods at large internuclear separations and the importance of non-additive non-interacting kinetic energy approximations at <i>all</i> separations.

What we can learn from exact embedding potentials of model systems

2019 Spring National Meeting

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