  Nanotubular materials inspired by crystalline diborides such as AlB_2 are
proposed. The atomic structure, in particular the basic chemical question of
where to put Al atoms in order to stabilize nanotubular Al-B systems, is
investigated using density-functional calculations for prototype systems. The
optimized tubular prototypes are found to be competitive in energy with their
bulk crystalline counterparts. All of the tubular Al-B systems investigated are
calculated to be metallic.
