The structure, stability, and electronic properties of the tenfold surface of the decagonal Al-Co-Ni quasicrystal have been investigated using ab initio density-functional methods. The structural model of the surface has been derived from the recently resolved structure of the $W\text{−}\left(\mathrm{Al}\mathrm{Co}\mathrm{Ni}\right)$ approximant phase. The bulk quasicrystal can be cleaved at the flat $A$ plane or at the puckered $B$ plane. We investigate the stability and electronic properties of the surface for both possible terminations. The simulated scanning-tunneling microscopy (STM) images of the $A$ and $B$ surfaces show that despite their significantly different atomic structure and chemical composition both surfaces exhibit quite similar STM images. The electronic structure of the approximant phase is characterized by a pseudogap at the Fermi level. The pseudogap at the surface is partially covered and the positions of $d$ bands of both transition metals undergo a substantial shift towards lower binding energies.

• Received 16 November 2005

DOI:https://doi.org/10.1103/PhysRevB.73.134203