Molecular dynamics simulations of 1/2 a(111) screw dislocation in Ta

Using a new, first principles based, embedded-atom-method (EAM) potential f or tantalum (Ta), we have carried out molecular dynamics (MD) simulations t o investigate the core structure, core energy and Peierls energy barrier an d stress for the 1/2 a <1 1 1 > screw dislocation. Equilibrated core struct ures were obtained by relaxation of dislocation quadrupoles with periodic b oundary conditions. We found that the equilibrium dislocation core has thre e-fold symmetry and spreads out in three <1 1 2 > directions on {1 1 0} pla nes. Core energy per Burgers vector b was determined to be 1.36 eV/b. We st udied dislocation motion and annihilation via molecular dynamics simulation s 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 (I 1 0) planes. Atoms forming the dislocation cores are distinguished based on t heir atomic energy. In this way, we can accurately define the core energy a nd its position not only for equilibrium configurations but also during dis location motion. Peierls energy barrier was computed to be similar to0.07 e V/b with a Peierls stress of similar to0.03 mu, where mu, is the bulk shear modulus of perfect crystal. The preferred slipping system at low temperatu re is <1 1 2 > directions and {1 1 0} planes. (C) 2001 Elsevier Science B.V . All rights reserved.