  Strongly correlated materials such as transition metal oxides (TMOs) often
exhibit large satellites in their x-ray photoemission (XPS) and x-ray
absorption spectra (XAS). These satellites arise from localized charge-transfer
(CT) excitations that accompany the sudden creation of a core hole. Here we use
a two-step approach to treat such excitations in a localized system embedded in
a condensed system and coupled to a photoelectron. The total XAS is then given
by a convolution of a spectral function representing the localized excitations
and the XAS of the extended system. The local system is modeled roughly in
terms of a simple three-level model, leading to a double-pole approximation for
the spectral function that represents dynamically weighted contributions from
the dominant neutral and charge-transfer excitations. This method is
implemented using a resolvent approach, with potentials, radial wave-functions
and matrix elements from the real-space Green's function code FEFF, and
parameters fitted to XPS experiments. Representative calculations for several
TMOs are found to be in reasonable agreement with experiment.
