  The stability of the perfect screw dislocation in silicon has been
investigated using both classical potentials and first-principles calculations.
Although a recent study by Koizumi et al . stated that the stable screw
dislocation was located in both the 'shuffle' and the 'glide' sets of {111}
planes, it is shown that this result depends on the classical potential used,
and that the most stable configuration belongs to the 'shuffle' set only, in
the centre of one hexagon. We also investigated the stability of an sp 2
hybridization in the core of the dislocation, obtained for one metastable
configuration in the 'glide' set. The core structures are characterized in
several ways, with a description of the three-dimensional structure,
differential displacement maps and derivatives of the disregistry.
