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 field is fully included, though only single scattering is considered at this stage. The total scattering cross sections demonstrate the importance of exchange-scattering processes in addition to direct scattering, even at higher energies of the scattering electron. The differential cross sections allow the investigation of angular, spin, and symmetry dependence for comparison with experiment. For certain transitions the angular dependence shows zeros associated with the point group symmetry of the Ni ion, and these are discussed. The ratio of spin-flip to non-spin-flip contributions is calculated exactly for multiplicity-changing transitions, and is shown to be independent of scattering geometry and energy of the incident electron