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Abstract

We present a detailed analysis of electronic properties of the Cockayne
model of icosahedral AlCuFe, both in its original form and after a
structural relaxation using the ab initio density functional approach.
The electronic density of states (DOS) and electric field gradients
(EFG's) of the Al and Fe atoms in the original and the relaxed Cockayne
models were calculated and compared with available photoemission,
Mossbauer, and nuclear quadrupole resonance spectroscopy data. The
relaxed and the original models show significantly different electronic
properties. Both models are deficient in describing the available
experimental data. The DOS's show two Fe-d peaks, where there is only
one such peak in the photoemission spectroscopy data. These models also
cannot account for the shape of the Mossbauer spectra. We show that the
interchange between 12 Cu and 12 Fe atoms, each belonging to a single
symmetry class, results in a smaller number of Cu-Fe nearest-neighbor
pairs and a lowering of the total energy by an amount of DeltaEsimilar
to50 meV/atom. This "modified" version of the Cockayne model was
further relaxed for the final comparison between the calculation and
experimental results. The modified model shows a considerable
improvement: The DOS has only one Fe-d peak, in agreement with
photoemission spectroscopy data, and the calculated EFG's account very
well for the experimental Mossbauer spectra.