R-matrix approach to low-energy electron energy-loss spectroscopy from NiO

Low-energy electron energy-loss spectra from NiO have been calculated using R-matrix methods to describe the excitation of 3d-3d transitions on the Ni ions. The effect of the crystal held is fully included, though only single scattering is considered at this stage. The total scattering cross section s demonstrate the importance of exchange-scattering processes in addition t o direct scattering, even at higher energies of the scattering electron. Th e differential cross sections allow the investigation of angular, spin, and symmetry dependence for comparison with experiment. For certain transition s the angular dependence shows zeros associated with the point group symmet ry of the Ni ion, and these are discussed. The ratio of spin-flip to non-sp in-flip contributions is calculated exactly for multiplicity-changing trans itions, and is shown to be independent of scattering geometry and energy of the incident electron.