Geometry controls the stability of FeSi14

Abstract

First-principles theoretical studies have been carried out to investigate the stability of Si_n cages impregnated with a Fe atom. It is shown that FeSi₉, FeSi₁₁, and FeSi₁₄ clusters exhibit enhanced local stability as seen through an increase in Si binding energy, Fe embedding energy, the gap between the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO), and the Ionization Potential (IP). The conventional picture for the stability of such species combines an assumption of electron precise bonding with the 18-electron rule; however, we find this to be inadequate to explain the enhanced stability in FeSi₁₁ and FeSi₁₄ because the d-band is filled for all FeSi_n clusters for n ≥ 9. FeSi₁₄ is shown to be the most stable due to a compact and highly symmetric Si₁₄ cage with octahedral symmetry that allows better mixing between Fe 3d- and Si 3p-electronic states.