  Site-occupation embedding theory (SOET) is a density-functional theory
(DFT)-based method which aims at modelling strongly correlated electrons. It is
in principle exact and applicable to model and quantum chemical Hamiltonians.
The theory is presented here for the Hubbard Hamiltonian. In contrast to
conventional DFT approaches, the site (or orbital) occupations are deduced in
SOET from a partially-interacting system consisting of one (or more) impurity
site(s) and non-interacting bath sites. The correlation energy of the bath is
then treated implicitly by means of a site-occupation functional. In this work,
we propose a simple impurity-occupation functional approximation based on the
two-level (2L) Hubbard model which is referred to as two-level impurity local
density approximation (2L-ILDA). Results obtained on a prototypical uniform
8-site Hubbard ring are promising. The extension of the method to larger
systems and more sophisticated model Hamiltonians is currently in progress.
