Calculating the Peierls energy and Peierls stress from atomistic simulations of screw dislocation dynamics: application to bcc tantalum

Abstract

We introduce a novel approach to calculating the Peierls energy barrier (and Peierls stress) based on the analysis of the dislocation migration dynamics, which we apply to 1/2a⟨111⟩ screw dislocations in bcc Ta. To study the migration of screw dislocations we use molecular dynamics with a first principles based embedded-atom method force field for Ta. We first distinguish the atoms belonging to the dislocation core based on their atomic strain energies, defining the dislocation core as the 12 atoms with higher strain energies per Burgers vector. We then apply this definition to the moving dislocations (following the dynamics of a [1−10] dipole of 1/2⟨111⟩ screw dislocations at 0.001 K) and extract their Peierls energy barrier (EP) and Peierls stress (τP). >From the dynamics of a dislocation dipole, we determine EP = 0.032 eV (and τP = 790 MPa) for twinning shear and EP = 0.068 eV (and τP = 1430 MPa) for anti-twinning shear, in good agreement with the results by applying direct shear stresses. This dislocation dynamics method provides insights regarding the dislocation migration process, allowing us to determine the continuous path of dislocation migration. We find that under twinning shear the screw dislocation moves along a path at an angle of only 8.5° with the [1−10] direction while for anti-twinning shear it moves along a path at an angle of 29.5° with the [1−10] direction, documenting the magnitude of the violation of the Schmid Law.