AB-INITIO STUDY OF POLYTETRAHEDRAL PACKING - THE AL-MG SYSTEM

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. © 1995 The American Physical Society.