  In a recent Letter [N. Lehto and S. Oberg, Phys. Rev. Lett. 80, 5568 (1998)],
Lehto and Oberg investigated the effects of strain fields on the core structure
of the 90-degree partial dislocation in silicon, especially the influence of
the choice of supercell periodic boundary conditions in theoretical
simulations. We show that their results for the relative stability between the
two structures are in disagreement with cell-size converged tight-binding total
energy (TBTE) calculations, which suggest the DP core to be more stable,
regardless of the choice of boundary condition. Moreover, we argue that this
disagreement is due to their use of a Keating potential.
