  The recently developed "internal" Density Functional Theory provides an
existence theorem for a local potential that contains the center-of-mass
correlations effects. The knowledge of the corresponding energy functional
would provide a much cheaper way than projection techniques to treat these
correlations. The aim of this article is to construct such a functional. We
propose a well-founded method, suitable for Fermions as well as for Bosons,
which does not require any free parameters.
