The role of reducing agents in the nucleation and growth of Al metalloid clusters: Ab initio molecular dynamic study.

Ab initio simulations are used to study the growth of metalloid aluminum clusters from their monohalide (AlCl) precursors. Molecular dynamics (MD) simulation is used to study the role of reducing agents in the growth process of Al metalloid clusters. Car-Parrinello MD simulations of AlCl liquid and Lithium-Aluminum Hydride reducing agent (LiAlH$_{\mathrm{4}})$ show spontaneous metalloid cluster growth. The growth process is initiated by transferring a proton to a nearby Al atom that helps forming trivalent impurities (AlCl$_{\mathrm{3}})$ in the solution. Growth towards larger metalloid clusters then proceeds via repeated insertion of AlCl into Al--Cl bonds as well as elimination of AlCl$_{\mathrm{3}}$ species. The transferred proton plays a significant role in reducing additional monohalide species from the solution. The energy barrier associated with the Al-Cl bond is dropped from 7.8 eV to 4 eV via proton-hopping between Al centers. However, this process is completely prohibited in the case of sodium borohydride (NaBH$_{\mathrm{4}})$ reducing agent due to strong Coulomb interactions between Na and B centers. Repeated insertion of additional AlCl monomers towards larger clusters was not observed within the same time scale of the previous simulations.