Structure and energetics of boron nitride fullerenes: The role of stoichiometry - art. no. 045402

We apply First-principles calculations to study the structure and the relat ive stability of several stoichiometric and nonstoichiometric boron nitride fullerenes of sizes ranging from 28 to 128 atoms. Among the structures con sidered, we observe an overall tendency for the formation of octahedrally f aceted shapes as the atomic number increases, with more spherical shapes be ing prevalent only for small nonstoichiometric cages. From these observatio ns, we expect that experimentally observed BN fullerenes of diameters of si milar to 12 Angstrom or larger to be polyhedrally faceted regardless of the ir stoichiometry. We also address the relative stability of the fullerenes in both nitrogen-rich and boron-rich environments. For the smaller molecule s, we find that the stoichiometric B16N16 is more stable than the nonstoich iometric structures with similar dimensions, in both environments. For the larger sizes, the nonstoichiometric B32N36 and B60N64 are found to be more stable than their stoichiometric counterparts in a nitrogen-rich environmen t, while the stoichiometric structures are the most stable under boron-rich conditions. These conclusions remain largely unchanged, when we consider t he gas-phase limit of atomic reservoirs.