  The geometrical and electronic structure properties of $<100>$ and $<110>$
silicon nanowires in the absence of surface passivation are studied by means of
density-functional calculations. As we have shown in a recent publication [R.
Rurali and N. Lorente, Phys. Rev. Lett. {\bf 94}, 026805 (2005)] the
reconstruction of facets can give rise to surface metallic states. In this
work, we analyze the dependence of geometric and electronic structure features
on the size of the wire and on the growth direction.

Mesoscale and Nanoscale Physics