  We present an ab initio theory of core- and valence resonant inelastic x-ray
scattering (RIXS) based on a real-space multiple scattering Green's function
formalism and a quasi-boson model Hamiltonian. Simplifying assumptions are made
which lead to an approximation of the RIXS spectrum in terms of a convolution
of an effective x-ray absorption signal with the x-ray emission signal.
Additional many body corrections are incorporated in terms of an effective
energy dependent spectral function. Example calculations of RIXS are found to
give qualitative agreement with experimental data. Our approach also yields
simulations of lifetime-broadening suppressed XAS, as observed in high energy
resolutionfluorescence detection experiment (HERFD). Finally possible
improvements to our approach are briefly discussed.
