Another figure related to dislocations, this time in tantalum (Ta). We have four <111> screw dislocations in the picture, here visualized with two superimposed plots. The while circles represent atomic positions. The black arrows form a "differential displacement map": an arrow between two atoms describes their mutual displacement from their ideal crystal positions due to the presence of the dislocation; following the arrow means positive net displacement along <111> and the length is proportional to the amount of displacement. Dislocation cores are easily visible as places where there is net circulation in the vector field. The superimposed color map shows the amplitude of the strain intensity field interpolated from the atomic displacements: as expected, dislocation cores are highly strained (red) compared to the background prefect crystal (blue). Reference: S. Ismail-Beigi and T. A. Arias, ``Ab Initio Study of Screw Dislocations in Mo and Ta: A new picture of plasticity in bcc transition metals'', Physical Review Letters 84, 1499 (2000).

Submitted by Sohrab Ismail-Beigi