PUBLICATION: M. Mihalkovic and M. Widom, "Tile-decoration model of the W-AlCoNi approximant", Phil. Mag. 86 (2005) p.557-65 (reprint)

ABSTRACT: We use ab-initio total energy calculations to refine chemical ordering of the W-AlCoNi approximant structure, and calculate its stability relative to other ternary and binary competing compounds. This approximant structure has 8A stacking periodicity along its pseudo-5-fold axis and can be interpreted as stacking of two identical adjacent 4A slabs with stacking vector inclined relative to the pseudo-5-fold axis. We generalize this stacking motif to model the 8A quasicrystal. Starting with 4A slabs forming a ``binary'' (3-level) decagonal tiling, we introduce tile flips between adjacent slabs analogous to the ``octagon'' tile-reshuffling update move for binary Penrose tiling. These tile flips lower the total energy, implying 8A superorder for the quasicrystal at low temperatures, consistent with experiment.