Atomic and electronic structure of crystalline and amorphous alloys. I. Calcium-magnesium compounds

Calculations of the atomic and electronic structure of Ca-Mg glasses and of the crystalline intermetallic compound ${\mathrm{CaMg}}_2$ are presented. For the glasses, the calculations are based on realistic models of the atomic structure constructed by a molecular-dynamics computer simulation linked to a steepest-descent potential-energy mapping. Interatomic forces are described in terms of pseudopotential-derived effective pair potentials. Our results for the atomic structure are in very good agreement with x-ray-diffraction data. They show that the topological short-range order in the glass is similar to the atomic arrangement in the crystalline Laves phase and best described as a highly defective tetrahedral close packing. The analogy between the glassy and the crystalline phases extends to the electronic structure. In both the crystalline and the amorphous alloys we find an essentially free-electron-like density of states (DOS), but close to the Fermi level the DOS is enhanced due to the onset of Ca 3d states. We find no evidence for the existence of a structure-induced minimum in the DOS near $E_F$. Our results are in good agreement with photoemission measurements and electronic specific-heat data.