Stress-dependent dislocation core structures leading to non-Schmid behavior

The stress-dependent core structures of dislocations for basal slip in magnesium are calculated using ab initio generalized stacking fault energy surface and microscopic phase-field method. The dissociation of dislocation cores exhibits the dependence on the non-shear component in the stress tensor; the Peierls stress is found to either become virtually zero or increase by an order of magnitude, depending on the applied shear stress magnitude and direction. The results, in contrast to the classical Schmid's law for crystal plasticity, are explained using the Escaig stress concept and the resulting implication on plastic deformation is discussed.