In the framework of the Density Functional Theory for superconductors,
we study the restoration of the particle number symmetry by means of
the projection technique. Conceptual problems are outlined
and numerical difficulties
are discussed. Both are related to the fact that neither the many-body
Hamiltonian nor the wave function of the system appear explicitly in the
Density Functional Theory. Similar obstacles are encountered in
self-consistent theories utilizing density-dependent effective interactions.
J. Dobaczewski,
M.V. Stoitsov,
W. Nazarewicz,
P.-G. Reinhard
August 8, 2007
