  By direct application of stress in molecular statics calculations we identify
the stress components that affect the glide of 1/2<111> screw dislocations in
bcc tungsten. These results prove that the hydrostatic stress and the normal
stress parallel to the dislocation line do not play any role in the dislocation
glide. Therefore, the Peierls stress of the dislocation cannot depend directly
on the remaining two normal stresses that are perpendicular to the dislocation,
as proposed by Koester A, Ma A, Hartmaier A. Acta Mater 2012;60:3894 but,
instead, on their combination that causes an equibiaxial tension-compression
(and thus shear) in the plane perpendicular to the dislocation line. The
Peierls stress of 1/2<111> screw dislocations then depends only on the
orientation of the plane in which the shear stress parallel to the Burgers
vector is applied and on the magnitude and orientation of the shear stress
perpendicular to the slip direction.
