Electronic structure calculations of Al-Cu alloys: comparison with experimental results on Hume-Rothery phases

Electronic band-structure calculations for a set of hypothetical Al-Cu allo ys are presented. The influence of the local order and of the Cu concentrat ion on the local density of states is analysed. The Als states are repelled towards the bottom of the occupied band by the interaction with the more l ocalized Cud states lying about 4 eV below the Fermi lever. Bonding and ant ibonding Al p states also appear, located on each side of the Cud band. The coupling between the more extended states of Al with the d band of Cu is w ell described by a Fano-like effect. Two calculations performed for real Al -Cu phases of the Hume-Rothery type allow direct comparison with experiment al results obtained by soft-X-ray spectroscopies. A pseudogap induced by th e interaction between the Fermi sphere and the Brillouin zone is observed i n agreement with the experiment. The availability of the Hume-Rothery crite rion in the formation of the pseudogap observed in quasicrystalline phases is also discussed.