  Dyson orbitals play an important role in understanding quasi-particle effects
in the correlated ground state of a many-particle system and are relevant for
describing the Compton scattering cross section beyond the frameworks of the
impulse approximation (IA) and the independent particle model (IPM). Here we
discuss corrections to the Kohn-Sham energies due to quasi-particle effects in
terms of Dyson orbitals and obtain a relatively simple local form of the
exchange-correlation energy. Illustrative examples are presented to show the
usefulness of our scheme.
