FIRST-PRINCIPLES MOLECULAR-DYNAMICS SIMULATION OF LIQUID MG3BI2

The liquid Mg-Bi system exhibits strong compound formation at the 'oct et' composition (Mg3Bi2) We present results of first-principles molecu lar dynamics simulations of this alloy system at different composition s: the pure Mg and Bi liquid components, the stoichiometric liquid, an d a Mg-rich composition (Mg62Bi28). For the pure liquids, our results are in excellent agreement with experimental diffraction data. For Mg3 Bi2, a significant modification of the characteristics of the local or dering is found w.r.t, the crystalline alpha-phase: the ordering in th e liquid is much more ionic. This structural modification is consisten t with the structure of the superionic beta-phase, that was reported r ecently by Barnes et al 1994 J. Phys.: Condens. Matter 6 L467. Our sim ulations cannot reproduce the 'reverse' metal-nonmetal transition obse rved upon melting, the computed conductivity being much larger than fo und in experiments. Instead, for the Mg-rich Mg62Bi28 alloy, the calcu lated conductivity approaches closely to the experimental value.