Prior to loading, NPT dynamics at T ¼ 1 K were performed
for 30 ps to relax the system and alleviate out-ofbalance
forces and net stresses. The system was then
loaded in shear by subjecting the atoms near the top
and bottom Y surfaces to a constant traction. For the
screw dislocation, the traction is syz. The applied traction
was increased at a constant quasi-static rate until
the dislocation broke free from the GP zone. At each
load step, nonlinear conjugate gradient minimization
was performed until the out-of-balance forces became
less than 108 eV/A˚ for the 0 K simulations. Molecular
dynamics simulations were performed using a standard
NVT approach.