  The Hubbard model is implemented in real-space Green's function calculations
of x-ray spectra using an effective self-energy adapted from the LSDA+U method
of Anisimov et al. This self-energy consists of an energy-dependent many-pole
approximation to the GW self-energy with an additive correction due to on-site
Coulomb repulsion among the partially filled localized-electron states. This
leads to a GW+U approach which provides an efficient procedure to account for
local correlation effects on x-ray spectra. Results are presented for the spin
and angular momentum projected density of states of MnO, NiO, and
La_(2-x)Sr_xCuO_4 (LSCO), for the K-edge x-ray spectra of O atoms in MnO and
NiO, and the unoccupied electronic states and O K-edge spectra of undoped LSCO.
The method is found to yield reasonable agreement with experiment.
