Structural and electronic properties of liquid Ge-Sn alloys:: Ab initio molecular-dynamics simulations

The structural and electronic properties of liquid Ge-Sn alloys are investigated by ab initio molecular-dynamics simulations. The calculated total static structure factors of liquid Ge0.8Sn0.2 alloys at 1273, 1523 and 1773 K are in good agreement with the recent experimental results obtained by the neutron scattering and their temperature dependence is very weak; with increasing temperature, the peak heights of the total structure factors and the partial radial distribution functions become slightly lower though their positions remain almost same. The long-wavelength limit of the concentration-concentration structure factor increases with decreasing temperature, which is consistent with the phase-separating tendency. The self-diffusion coefficients for Ge and Sn atoms in liquid Ge0.8Sn0.2 alloys are obtained from the calculated velocity autocorrelation functions and the mean square displacements and are compared with those values calculated by ab initio molecular-dynamics simulation for pure liquid Ge and Sn, respectively. The total and partial electronic densities of states obtained by our simulation do not depend on the temperature and show that the liquid alloys considered in this paper are metallic, though the coexistence of the covalent-like and 'metallic' bonds is shown by the analyses of the maximally localized Wannier functions.