  We report the prediction of metallic quasione-dimensional $sp^{3}$-hybridized
silicon allotropes in the form of prismanes. Silicon prismanes or
polysilaprismanes are the silicon nanotubes of a special type constructed from
the dehydrogenated molecules of cyclosilanes (silicon rings). By means of
density functional theory the electronic, geometry, energy, and some mechanical
properties of these tubes were investigated. Our results show that silicon
polyprismanes are thermodynamically stable compounds, and the character of the
energy spectrum, as well as the behavior of transmission function near the
Fermi level, show that they exhibit non-typical for the silicon systems
metallic nature. Moreover, the metallic state of polysilaprismanes is resistant
to the mechanical stresses applied along their main axis. Unusual properties
predicted in the presented study discover new prospects of application of
silicon nanostructures as the basic elements of future micro- and
nanoelectronics, as well as in energy, metrology, medical, and information
technologies.
