Chemical ordering in Al72Ni20Co8 decagonal quasicrystals

First-principles total energy calculations of the 2-nm clusters seen in hig h-perfection Al72Ni20Co8 decagonal quasicrystals demonstrate that chemical ordering between Al and transition metals in the central ring is energetica lly highly favorable. The chemical ordering introduces extensive structure relaxation and results in broken decagonal symmetry. Such broken symmetry i s sufficient to enforce the perfect quasiperiodic tiling.