Density functional calculations for Zintl systems: structure, electronic structure and electrical conductivity of liquid NaSn alloys

Molecular dynamics (MD) simulations are presented for five different compositions of liquid NaSn alloys, covering the range from 20 to 80% sodium. We apply an ab initio (Car-Parrinello) method as well as an approximate LCAO-DFT scheme. The two methods yield similar results: the tin atoms form large dynamic networks. Only for the sodium-rich composition are isolated tin atoms and dimers observed.

From the ab initio MD trajectories the structure factors, the total and partial densities of states, the charge distributions and, by means of the Kubo-Greenwood formula, the electrical conductivities are calculated. The structure factors and the conductivities are obtained as functions of the composition and show good agreement with experimental data.

We give a detailed discussion of the concentration dependence of the structure factors, the total and partial densities of states, the charge distributions and the electrical conductivities. The behaviour and the origin of the prepeak is discussed. For the equimolar composition the dependence of the conductivity on temperature is obtained and is in qualitative accord with experimental data.