Core energy and Peierls stress of a screw dislocation in bcc molybdenum: A periodic-cell tight-binding study

Using a formulation based on anisotropic elasticity we determine the core energy and Peierls stress of the a₀∕2[111] screw dislocation in bcc molybdenum at $T=0$. We show that a proper definition of the core energy necessarily involves choosing a reference direction ̂ \^a and a reference radius r₀ in order to describe dislocation dipole rotation and dilatation respectively in the asymptotic expansion of the total energy. The core energy is extracted from atomistic calculations for supercells containing a single dislocation dipole with periodic boundary conditions in a manner that treats fully consistently the effects of image interactions, such that the core energy extracted is invariant with respect to the supercell size and shape, image-sum aspect ratio, and dislocation dipole distance and orientation. Using an environment-dependent tight-binding model we obtain 0.3710.3em0exeV∕ at ̂ \^a=⟨112̄⟩ and r₀=b and 3.80.3em0exGPa for the energy of a core with zero polarity and Peierls stress for simple shear in (1̄10)⟨111⟩, respectively, to be compared to 0.3000.3em0exeV∕ and 2.40.3em0exGPa obtained using an empirical many-body potential for a polarized core. Our results suggest that the large Peierls stress of screw dislocation in Mo is due to the transition from nonplanar to planar core, rather than a direct effect of the equilibrium core polarity.