Atomistic simulation of single kinks of screw dislocations in α-Fe

We have studied the structure and the formation and migration energies of single kinks in 1/2<1 1 1> screw dislocations in body-centered cubic iron, by performing static calculations using the Ackland-Mendelev empirical potential, which correctly accounts for the non-degenerate core structure. The methodology for constructing simulation cells with fully periodic boundary conditions based on the quadrupolar arrangement of dislocation dipoles, with a single kink on each dislocation line is presented. The two types of kinks - left and right - are found to have similar widths, namely ∼20 Burgers vectors. The convergences of the formation energies with cell-size along the dislocation line, as well as with the distance between the two dislocations are investigated. A dependence proportional to the inverse of the distance between kinks along the dislocation line is found when kinks overlap. The formation energies of the left and right kinks are significantly different: 0.57 and 0.08 eV, respectively. The Peierls potentials of the second kind are evaluated with the drag method: the energy barriers are found to be lower than 0.1 meV for both kinks.