  We use \textit{ab initio} molecular dynamics simulations to investigate the
properties of the dry surface of pure silica and sodium silicate glasses. The
surface layers are defined based on the atomic distributions along the
direction ($z-$direction) perpendicular to the surfaces. We show that these
surfaces have a higher concentration of dangling bonds as well as two-membered
(2M) rings than the bulk samples. Increasing concentration of Na$_2$O reduces
the proportion of structural defects.
  From the vibrational density of states, one concludes that 2M rings have a
unique vibrational signature at a frequency $\approx850$~cm$^{-1}$, compatible
with experimental findings.
  We also find that, due to the presence of surfaces, the atomic vibration in
the $z-$direction is softer than for the two other directions. The electronic
density of states shows clear the differences between the surface and interior
and we can attribute these to specific structural units. Finally, the analysis
of the electron localization function allows to get insight on the influence of
local structure and the presence of Na on the nature of chemical bonding in the
glasses.
