Ab initiostudy of polytetrahedral packing: The Al-Mg system

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Abstract
We have performed first-principles local-density-approximation calculations on aluminum-magnesium intermetallic compounds. Experimental studies of this system have shown that complex topologically close-packed structures with large unit cells are favored over simpler planar structures. We show that this is due to the opening of a quasigap in the density of states at the Fermi level; our results for total energies confirm that this lowers the energy. These electronic effects resemble those measured and calculated for quasicrystals which have similar chemical compositions and structures.