Prediction of Dislocation Cores in Aluminum from Density Functional Theory

The strain field of isolated screw and edge dislocation cores in aluminum are calculated using density-functional theory and a flexible boundary condition method. Nye tensor density contours and differential displacement fields are used to accurately bound Shockley partial separation distances. Our results of 5–7.5 Å (screw) and 7.0–9.5 Å (edge) eliminate uncertainties resulting from the wide range of previous results based on Peierls-Nabarro and atomistic methods. Favorable agreement of the predicted cores with limited experimental measurements demonstrates the need for quantum mechanical treatment of dislocation cores.

Figure 1

Atomic core structure (screw and edge components) of the two partials of the $a/2[110]$ screw-character dislocation. The atomic positions (circles) are superimposed on the differential displacements (arrows) and the Nye tensor distribution (color map); see text for details. Using the screw components, the triad of arrows with a net chirality identifies the position of the partials whose separation is $d_s^{\mathrm{DD}}$. From the edge components, the centers of the partials are identified as the extrema in the Nye tensor distribution whose separation is $d_s^{\mathrm{Nye}}$. Using these two measurements the partial core separation is shown to be in the range of 5.0–7.5 Å.

Figure 2

Atomic core structure (edge and screw components) of the two partials of the $a/2[110]$ edge-character dislocation. As in Fig. 1 the atomic positions (circles) are superimposed on the differential displacements (arrows) and the Nye tensor distribution (color map). Using the edge components, the triad of arrows with a net chirality identifies the position of the partials whose separation is $d_e^{\mathrm{DD}}$. From the screw components, the center of the partials is identified as the extrema in the Nye tensor distribution whose separation is $d_e^{\mathrm{Nye}}$. Using these two measurements the partial core separation is shown to be in the range of 7.0–9.5 Å.