Copper tubules and local origin of a pseudogap in d-AlCuCo from ab initio calculations

We examined in great detail various stoichiometric variants of the Burkov model based on the Tubinger triangle tiling. We present density of states calculated with the linear muffin-tin-orbital method in the atomic sphere approximation (LMTO-ASA) method on 1/1 approximants. We define a subset of the Burkov model which exhibits a clear pseudogap at the Fermi level, as shown in measurements of photoemission spectra. All the resulting systems contain pure copper tubules in the direction perpendicular to the quasicrystalline plane. We show that the appearance of a gap is due to two distinct mechanisms: A Hume-Rothery-like one for the s and p slates and a Al-sp-Co-d hybridization in certain cobalt clusters, leading to a wide splitting of the d slates at that specific site. We comment on the spiky structure of the presented density of stales (DOS) and the projected DOS and demonstrate the artificial appearance of spikes in LMTO-ASA calculations on simple model systems. [S0163-1829(98)07225-7].