  We demonstrate that the straightforward application of the Nudged Elastic
Band (NEB) method does not determine the correct Peierls barrier of 1/2<111>
screw dislocations in BCC metals. Although this method guarantees that the
states (images) of the system are distributed uniformly along the minimum
energy path, it does not imply that the dislocation positions are distributed
uniformly along this path. In fact, clustering of dislocation positions near
potential minima occurs which leads to an overestimate of both the slope of the
Peierls barrier and the Peierls stress. We propose a modification in which the
NEB method is applied only to a small number of degrees of freedom that
determine the position of the dislocation, while all other coordinates of atoms
are relaxed by molecular statics as in any atomistic study. This modified NEB
method with relaxations gives the Peierls barrier that increases smoothly with
the dislocation position and the corresponding Peierls stress agrees well with
that evaluated by the direct application of stress in the atomistic modeling of
the dislocation glide.
