The first ab initio density-functional study of <111> screw dislocation cores in these body-centered cubic transition metals were reported. The results suggested a new view of body-centered cubic plasticity; with symmetrical and compact dislocation cores. This was contrary to the currently accepted view, which was based upon continuum and interatomic potentials. The levels of core energy according to this new view were in much better agreement with the Peierls energy barriers to dislocation motion which were indicated by experiment.

Ab initio Study of Screw Dislocations in Mo and Ta - a New Picture of Plasticity in BCC Transition Metals. S.Ismail-Beigi, T.A.Arias: Physical Review Letters, 2000, 84[7], 1499-502