Effect of alloying on screw dislocation structure in Mo: atomistic modelling approach with ab-initio parametrization

The plastic deformation in bcc metals is realized by the motion of screw dislocations with a complex star-like non-planar core. In this case, the direct investigation of the solute effect by first principles electronic structure calculations is a challenging problem for which we follow a combined approach that includes atomistic dislocation modelling with {\it ab-initio} parametrization of interatomic interactions. The screw dislocation core structure in Mo alloys is described within the model of atomic row displacements along a dislocation line with the interatomic row potential estimated from total energy full-potential linear muffin-tin orbital (FLMTO) calculations with the generalized gradient approximation (GGA) for the exchange-correlation potential. We demonstrate (1) that the solute effect on the dislocation structure is different for ``hard'' and ``easy'' cores and (2) that the softener addition in a ``hard'' core gives rise to a structural transformation into a configuration with a lower energy through an intermediate state. The softener solute is shown to disturb locally the three-fold symmetry of the dislocation core and the dislocation structure tends to the split planar core.