Molecular dynamics simulations of 1/2 a〈1 1 1〉 screw dislocation in Ta

Abstract

Using a new, first principles based, embedded-atom-method (EAM) potential for tantalum (Ta), we have carried out molecular dynamics (MD) simulations to investigate the core structure, core energy and Peierls energy barrier and stress for the 1/2 a〈1 1 1〉 screw dislocation. Equilibrated core structures were obtained by relaxation of dislocation quadrupoles with periodic boundary conditions. We found that the equilibrium dislocation core has three-fold symmetry and spreads out in three 〈1 1 2〉 directions on {1 1 0} planes. Core energy per Burgers vector b was determined to be 1.36 eV/ b. We studied dislocation motion and annihilation via molecular dynamics simulations of a periodic dislocation dipole cell, with 〈1 1 2〉 and 〈1 1 0〉 dipole orientation. In both cases the dislocations move in zigzag on primary {1 1 0} planes. Atoms forming the dislocation cores are distinguished based on their atomic energy. In this way, we can accurately define the core energy and its position not only for equilibrium configurations but also during dislocation motion. Peierls energy barrier was computed to be ∼0.07 eV/ b with a Peierls stress of ∼0.03 μ, where μ is the bulk shear modulus of perfect crystal. The preferred slipping system at low temperature is 〈1 1 2〉 directions and {1 1 0} planes.