The formation energy of kink pairs in dissociated screw dislocations in the {111} planes of fcc lattices is studied with Cu as an example. The two Shockley partials are represented by Peierls dislocations separated by the splitting width d. The misfit energy in the glide plane is obtained from the gamma surface. The Peierls energy is derived by shifting the centre of the dislocation and numerical summing the misfit energy at the position of the atom rows parallel to the dislocation line. There exists a number of stable equilibrium configurations with different separations d(i). If the separation of the partials stays constant as they move, the periodicity of the Peierls potential is equal to the distance a between atom rows. When, however, the separation between the partials is allowed to vary, there exist minima in the potential at multiples of a/2. There can exist normal kink pairs of height a and, under certain conditions, fractional kink pairs of height close to a/2 with less than half the formation energy of normal kink pairs. [References: 31]
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