Atomistic simulations of (a/2)⟨111⟩ screw dislocations in bcc Mo using a modified generalized pseudopotential theory potential

Atomistic simulations using a modified generalized pseudopotential theory potential and Green's function boundary conditions were employed to determine the Peierls stress of rigid straight (a/2) [111] screw dislocations for the application of shear stresses on {110}- and {112}-type planes in bcc Mo. It is found that the Peierls stress of (a/2) [111] screw dislocations for the application of shear stress on the {110} planes is (0.0175-0.020)mu. Large twinning-antitwinning asymmetry is found for the application of pure shear stress on the {112} planes with the Peierls stress along the twinning direction being (0.0125-0.020)mu and along the antitwinning direction to be (0.050-0.0562)mu. The Peierls stress of screw dislocations for the application of tensile and compressive stresses along {001}, {110}, {111} and {201} directions were also determined. A large tension-compression asymmetry is observed for the {001}, {110} and {111} directions. This is a manifestation of the twinning-antitwinning asymmetry observed in the pure shear stress calculations. A tension-compression asymmetry is also observed for the {201} direction, indicating that non-glide stress effects are also important in determining the Peierls stress. To facilitate an understanding of (a/2) [111] screw dislocation motion by the kink pair mechanism, the core structure and energetics of six possible kinks and two antiphase defects on (a/2) [111] screw dislocations were also determined. It is found that the kink pair formation energy at infinite separation distance varies between 1.46 and 2.10 eV, which is in reasonable accord with the experimental value of 1.27 eV.