Concentration dependence of structural and bonding properties of liquid Tl-Se alloys byab initiomolecular dynamics simulations

Abstract

The structural and electronic properties of liquid ${\text{Tl}}_{x}{\text{Se}}_{1\ensuremath{-}x}$ for $0\ensuremath{\le}x\ensuremath{\le}1$ are investigated by means of ab initio molecular dynamics simulations. It is shown that calculated structure factors are in good agreement with experiments over the whole range of composition. It is confirmed from calculated electronic densities of states that the liquid Tl-Se alloys have semiconducting properties for Tl concentrations not exceeding the stoichiometric composition $(x=2/3)$, while they are metallic for $x>2/3$. In Se-rich composition range, Se atoms form chain molecules, whose average length becomes shorter with increasing Tl concentration. In the equiatomic liquid Tl-Se alloy, short Se chains, mostly negatively charged ${\text{Se}}_{2}$ dimers, coexist with a few Se ions, while most of Se atoms exist as ions at the stoichiometric composition. Based on a population analysis, we discuss the concentration dependence of the bonding properties in comparison with that in liquid alkali-metal chalcogenides.