Flexible boundary condition for a moving dislocation

It is well known that a boundary condition usually affects the result of the computer simulation of defects, especially extended defects like a straight dislocation, where the model size dependence of the result is sometimes observed. In order to solve this problem, a flexible boundary condition is developed for the simulation of a moving dislocation by applying the Lagrange principle in the present study. Under the flexible boundary condition described here, various properties of a screw dislocation, i.e., stable core structure, Peierls stress and glide property, are calculated in a square lattice and the model size dependence of the result is hardly obtained over a wide range. Contrary to the present flexible boundary condition, explicit size dependence is observed in the case of a rigid boundary condition due to a strong image force from the boundary. It is observed, however, that the result tends to approach that obtained in the above flexible boundary model as the size of the model lattice increases. Unfortunately, in the case of a screw dislocation with higher Peierls stress than 10^-2G, the flexible boundary condition is not available, because lattice vibrations with a high frequency are emitted from the dislocation line during glide motion and the boundary cannot respond to these waves.