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

2004; American Physical Society; Volume: 70; Issue: 10 Linguagem: Inglês

10.1103/physrevb.70.104113

1550-235X

Ju Li, Cai‐Zhuang Wang, Jinpeng Chang, Wei Cai, Vasily V. Bulatov, Kai‐Ming Ho, Sidney Yip,

Fusion materials and technologies

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 $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\mathbf{a}}$ 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 $0.371\phantom{\rule{0.3em}{0ex}}\mathrm{eV∕\AA{}}$ at $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\mathbf{a}}=⟨11\overline{2}⟩$ and ${r}_{0}=b$ and $3.8\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ for the energy of a core with zero polarity and Peierls stress for simple shear in $(\overline{1}10)⟨111⟩$, respectively, to be compared to $0.300\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\AA{}$ and $2.4\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ obtained using an empirical many-body potential for a polarized core. Our results suggest that the large Peierls stress of screw dislocation in $\mathrm{Mo}$ is due to the transition from nonplanar to planar core, rather than a direct effect of the equilibrium core polarity.