  Finite magnesium oxide nanotubes are investigated. Stacks of four parallel
squares, hexagons, octagons, and decagons are constructed and studied by the
pseudopotential density functional theory within the local-density
approximation. Optimized structures are slightly distorted stacks of polygons.
These clusters are insulators and the band gap of 8.5 eV is constant over an
investigated range of the diameters of stacked polygonal rings. Using the
L"owdin population analysis a charge transfer towards the oxygen atoms is
estimated as 1.4, which indicates that the mixed ionocovalent bonding exists in
investigated MgO nanotubes.
