Ab initio simulations of liquid NaSn alloys: Zintl anions and network formation

TL;DR

This study uses ab initio molecular dynamics to explore the structure and cluster formation in liquid NaSn alloys, revealing network formation of tin atoms and agreement with experimental scattering data.

Contribution

First ab initio simulations of liquid NaSn alloys showing detailed structural insights and cluster dynamics across various compositions.

Findings

Structure factors match neutron scattering data.

Sn atoms form networks at certain compositions.

Isolated tin clusters are unstable in these liquids.

Abstract

Using the Car-Parrinello technique, ab initio molecular dynamics simulations are performed for liquid NaSn alloys in five different compositions (20, 40, 50, 57 and 80 % sodium). The obtained structure factors agree well with the data from neutron scattering experiments. The measured prepeak in the structure factor is reproduced qualitatively for most compositions. The calculated and measured positions of all peaks show the same trend as function of the composition.\\ The dynamic simulations also yield information about the formation and stability of Sn$_4$ clusters (Zintl anions) in the liquid. In our simulations of compositions with 50 and 57 % sodium we observe the formation of networks of tin atoms. Thus, isolated tin clusters are not stable in such liquids. For the composition with 20 % tin only isolated atoms or dimers of tin appear, ``octet compounds'' of one Sn atom surrounded by 4 Na atoms are not observed.