AB-INITIO SIMULATIONS OF LIQUID NASN ALLOYS - ZINTL ANIONS AND NETWORK FORMATION

Using the Car-Parrinello technique, ab initio molecular dynamics simul ations are performed for liquid NaSn alloys in five different composit ions (20, 40, 50, 57 and 80% sodium). The obtained structure factors a gree well with the data from neutron scattering experiments. The measu red prepeak in the structure factor is reproduced qualitatively for mo st compositions. The calculated and measured positions of all peaks sh ow the same trend as function of the composition. The dynamic simulati ons also yield information about the formation and stability of Sn4 cl usters (Zintl anions) in the liquid. In our simulations of composition s with 50 and 57% sodium we observe the formation of networks of tin a toms. Thus, isolated tin clusters are not stable in such liquids. For the composition with 20% tin only isolated atoms or dimers of tin appe ar; 'octet compounds' of one Sn atom surrounded by four Na atoms are n ot observed.