At. Paxton et al., The near-edge structure in energy-loss spectroscopy: many-electron and magnetic effects in transition metal nitrides and carbides, J PHYS-COND, 12(5), 2000, pp. 729-750
We investigate the ability of the local density approximation (LDA) in dens
ity functional theory to predict the near-edge structure in electron energy
-loss spectroscopy in the dipole approximation. We include screening of the
core hole within the LDA using Slater's transition state theory. We find t
hat anion K-edge threshold energies are systematically overestimated by 4.2
2 +/- 0.44 eV in twelve transition metal carbides and nitrides in the rock-
salt (B1) structure. When we apply this 'universal' many-electron correctio
n to energy-loss spectra calculated within the transition state approximati
on to LDA, we find quantitative agreement with experiment to within one or
two eV for TiC, TiN and VN. We compare our calculations to a simpler approa
ch using a projected Mulliken density which honours the dipole selection ru
le, in place of the dipole matrix element itself. We find remarkably close
agreement between these two approaches. Finally, we show an anomaly in the
near-edge structure in CrN to be due to magnetic structure. In particular,
we find that the N K edge in fact probes the magnetic moments and alignment
s of ther sublattice.