Finite temperature behavior of impurity doped Lithium cluster {\em viz} Li$_6$Sn

TL;DR

This study uses ab initio molecular dynamics to analyze how impurity doping with Sn affects the finite temperature properties and melting behavior of lithium clusters, revealing significant changes in thermal stability and specific heat features.

Contribution

It provides new insights into the thermal behavior of Li clusters doped with Sn, highlighting the impact of charge transfer and bond weakening on melting temperatures and specific heat characteristics.

Findings

Li6Sn melts around 250 K, lower than Li7 at 425 K.

Charge transfer from Li to Sn weakens Li-Li bonds.

Li6Sn exhibits a shoulder in specific heat at 50 K due to quasirotational motion.

Abstract

We have carried out extensive isokinetic {\it ab initio} molecular dynamic simulations to investigate the finite temperature properties of the impurity doped cluster Li$_6$Sn along with the host cluster Li$_7$. The data obtained from about 20 temperatures and total simulation time of at least 3 ns is used to extract thermodynamical quantities like canonical specific heat. We observe a substantial charge transfer from all Li atoms to Sn which inturn weakens the Li-Li bonds in Li$_6$Sn compared to the bonds in Li$_7$. This weakening of bonds changes the finite temperature behavior of Li$_6$Sn significantly. Firstly, Li$_6$Sn becomes liquid-like around 250 K, a much lower temperature than that of Li$_7$ ($\approx$~425 K). Secondly, an additional quasirotational motion of lithium atoms appears at lower temperatures giving rise to a shoulder around 50 K in the specific heat curve of Li$_6$Sn. The peak in the specific heat of Li$_7$ is very broad and the specific heat does not show any premelting features.