Occupancy of central sites in the Zn₄₉Mg₃₂ quasicrystal from total-energy computations on its crystal approximant

Abstract

First-principles electronic-structure and total-energy calculations related to the 1/1 crystal approximant to the Al-Zn-Mg quasicrystal are carried out with different possible atoms at the center of the packing unit. The linear muffin-tin-orbital (LMTO) method with the atomic-sphere approximation and the muffin-tin correction to the Coulomb energy is employed. The density of states shows a very shallow minimum near the Fermi level, supporting the view that the pseudogap exists in the crystal approximants to quasicrystals even in the absence of a d-state contribution to the valence electrons. It is shown that packing units with Al or Zn at the centers are more stable than those with empty centers, supporting the recent positron-annihilation data and pseudopotential calculations, but disagreeing with qualitative conclusions from some LMTO calculations for crystal approximants to other quasicrystals.