Electronic structure of fullerene-like cages and finite nanotubes of aluminum nitride

We report density functional study of alternate fullerene-like cage structures and finite closed, capped single-wall nanotubes of aluminum nitride. The cages and nanotubes studied are modeled as Al24N24, Al28N28, Al32N32, Al36N36, Al48N48, and Al96N96. The structure optimization and calculation of the electronic structure, vertical ionization potential, and the electron affinity are performed at the all electron level by the analytic Slater-Roothaan method, using polarized Gaussian basis set of double zeta quality. All structures are energetically stable with binding energy of about 10-11 eV per AlN pair. For the larger Al96N96, the fullerene like cage is energetically less favorable than the two-shell cluster that has Al24N24 as an inner shell. The vertical ionization potential and the electronic affinity are in the range 6.7-6.9 eV and 1.5-2.0 eV, respectively. The binding energy show systematic increase with increase in the length of (4,4) nanotube. The energy band gap, determined using the ∆SCF method show that these structures are characterized by a fairly large band gap about 4−5 eV, which is however smaller than the gap for the corresponding boron nitride structures.