Structure and stability of M₆N₈ clusters (M = Si, Ge, Sn, Ti)

The structures and stabilities of the M₆N₈ clusters (M = Si, Ge, Sn, Ti) have been theoretically studied at DFT and ab initio levels of theory. Two new isomers have been considered: cage-like molecules and propeller-like molecules. It is shown that only for M = Si are both isomers true minima on the potential energy surface. The thermodynamics of the dissociation process ¹/₆M₆N₈ →¹/ ₃M₃N₄ is discussed. For each M ₃N₄ molecule, four structures with different multiplicity are considered. The thermodynamic analysis shows that independently of the multiplicity of M₃N₄ nitrides all M₆N ₈ clusters are stable in the gas phase in a wide temperature range and could be potential intermediates in chemical vapor deposition of the nitride materials.