For SIA diffusion in a bulk material, only atoms near the SIA can be attributed to the positional change of the SIA, while all of the other atoms vibrate near their equilibrium positions.
Therefore, the bias potential only needs to be applied to the SIA and its neighbors. In the present hyper-MD simulation, the local bias potential was simply added to only the SIA and the two nearest-neighbor atoms with have higher energies compared to the other atoms. To describe the atomic interaction in a-iron, the empirical interatomic potential developed by Mendelev et al.