  We discuss recent Cu K-edge resonant inelastic scattering (RIXS) results for
CuB2O4, a model system consisting of electronically-isolated CuO4 plaquettes,
which exhibits anomalies in the incident photon energy dependence that are not
captured by electron-only models. We show that these anomalous features can be
qualitatively described by extending the electron-only considerations to
include the lattice degrees of freedom. Our findings have important general
implications for the interpretation of K-edge RIXS results for electronically
higher-dimensional transition metal oxides.
