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 a(0)/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 r(0) 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 0.371 eV/Angstrom at (a) over cap=<11 (2) over bar > and r(0)=b and 3.8 GPa for the energy of a core with zero polarity and Peierls stress for simple shear in ((1) over bar 10)<111>, respectively, to be compared to 0.300 eV/Angstrom and 2.4 GPa 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.