Geometric, electronic properties and the thermodynamics of pure and Al--doped Li clusters

TL;DR

This study uses first-principles simulations to explore how aluminum doping affects the structure, electronic properties, and melting behavior of small lithium clusters, revealing significant changes with increased Al content.

Contribution

It provides new insights into the structural and thermodynamic effects of Al doping in Li clusters, highlighting the impact on bonding and melting characteristics.

Findings

Al doping causes structural rearrangements in Li clusters.

Two Al atoms induce surface melting of Li atoms.

Al atoms form weak covalent bonds, affecting melting behavior.

Abstract

The first--principles density functional molecular dynamics simulations have been carried out to investigate the geometric, the electronic, and the finite temperature properties of pure Li clusters (Li$_{10}$, Li$_{12}$) and Al--doped Li clusters (Li$_{10}$Al, Li$_{10}$Al$_2$). We find that addition of two Al impurities in Li$_{10}$ results in a substantial structural change, while the addition of one Al impurity causes a rearrangement of atoms. Introduction of Al--impurities in Li$_{10}$ establishes a polar bond between Li and nearby Al atom(s), leading to a multicentered bonding, which weakens the Li--Li metallic bonds in the system. These weakened Li--Li bonds lead to a premelting feature to occur at lower temperatures in Al--doped clusters. In Li$_{10}$Al$_2$, Al atoms also form a weak covalent bond, resulting into their dimer like behavior. This causes Al atoms not to `melt' till 800 K, in contrast to the Li atoms which show a complete diffusive behavior above 400 K. Thus, although one Al impurity in Li$_{10}$ cluster does not change its melting characteristics significantly, two impurities results in `surface melting' of Li atoms whose motions are confined around Al dimer.