The fundamental atomic-scale properties of (a/2)<111> screw dislocations and other defects were simulated by using new quantum-based multi-ion interatomic potentials which were derived from a model generalized pseudopotential theory. The potentials were checked by using a combination of experimental data and ab initio electronic structure calculations of ideal shear strength, vacancy and self-interstitial formation and migration energies, grain-boundary atomic structures and generalized stacking-fault energy surfaces. Accurate 2- and 3-dimensional Green’s function techniques were used to relax the boundary forces dynamically during dislocation simulations. The Green’s function techniques were combined with a spatial domain decomposition strategy. resulting in a parallel generalized pseudopotential atomistic simulation code which increased the computational performance by 2 orders of magnitude. The dislocation simulations predicted the existence of a degenerate core structure, with three-fold symmetry, but it was one that was nearly isotropic and only weakly polarized at ambient pressures. The degenerate nature of the core structure led to possible antiphase defects on the dislocation line, as well as multiple possible dislocation kinks and kink pairs. The antiphase defects and kink energetics were determined in detail for the low-stress limit. In this limit, the calculated stress-dependent activation enthalpy for the lowest-energy kink pair agreed well with that currently used, in mesoscale dislocation dynamics simulations, to model the temperature-dependent single-crystal yield stress. In the high-stress limit, the calculated Peierls stress exhibited a marked orientational dependence under pure shear and uniaxial loading conditions; with an anti-twinning/twinning ratio of 2.29 for pure shear {211}-<111> loading.

Accurate Atomistic Simulation of (a/2) <111> Screw Dislocations and Other Defects in BCC Tantalum. L.H.Yang, P.Soderlind, J.Moriarty: Philosophical Magazine A, 2001, 81[5], 1355-85