ELECTRONIC-STRUCTURE AND STABILITY OF A MODEL OF THE DECAGONAL QUASI-CRYSTAL AL-CU-CO

We present an electronic structure study of a model of the decagonal quasicrystal Al-Cu-Co, proposed by one of us (SEE). Both quasicrystalline clusters and their crystalline counterparts are examined. The locations and the ratio of the concentrations of Cu and Co atoms in the model are found to be important in determining the shape and the magnitude of the density of states at the Fermi level. A local minimum in the density of states (DOS) at the Fermi level is exhibited only by clusters with a Cu concentration larger than Co. However, such clusters do not have the lowest internal (band) energy. No DOS minimum at the Fermi level is obtained for clusters with equal or nearly equal Cu and Co concentrations. Spectral functions reveal no evidence of a pseudogap originating from a Fermi-surface-Jones-zone-boundary interaction. Eigenstates at the Fermi level do not appear localized within the clusters used in our calculations.