  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 "Delta 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.
