F. Catara et al., TOWARDS A SELF-CONSISTENT RANDOM-PHASE-APPROXIMATION FOR FERMI SYSTEMS, Physical review. B, Condensed matter, 54(24), 1996, pp. 17536-17546
We present a method which allows us to treat correlations in finite Fe
rmi systems in a more consistent way than the random-phase approximati
on (RPA). The quasiboson approximation (QBA), where expectation values
in the ground state of the system are approximated by their values in
the uncorrelated reference state, is avoided in our approach where th
e correlated ground state is always used. We derive a closed, nonlinea
r set of equations which determines the energies and wave functions of
the excited states as well as the single-particle occupation numbers
in the ground state. As an example we apply to metallic clusters a sim
plified version of the approach which represents, however, a significa
nt improvement over previous attempts to go towards a self-consistent
RPA. We show that our method allows one to correct for the inadequacy
of standard RPA in cases where the use of QBA becomes questionable.