Atomic simulation of the dislocation core structure and Peierls stress in alkali halide

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Abstract
Dislocation core behaviour was studied by determining the equilibrium arrangement of ions surrounding an a/2〈110〉 {110} edge dislocation in potassium chloride. A computer simulation method was used to solve the equations of motion of the ions interacting through a Coulombic potential, with a Born-Mayer repulsive contribution, between nearest neighbours. Two flexible boundary schemes were employed and their application and importance to the results are described. The observed difference between the Volterra description of the ion positions and the calculated equilibrium position constitutes the core field. This core field was examined in detail but its most important feature is a lattice expansion of about 0-5 b2 per unit dislocation length. Shear stresses were also applied to the models using flexible boundary conditions with results indicating a Peierls stress in the range of 12-7 to 32-4 MPa which is in reasonable agreement with experiment. The case of moving the dislocation was quite sensitive to boundary conditions. Some implication of possible core field effects, including interaction with other defects and coupling with the full stress tensor to influence the Peierls stress, are discussed.