Energy pathways and directionality in deformation twinning

We present ab initio density functional theory calculations of twinning energy pathways for two opposite twinning modes, (111) [11 2-] and (111) [1- 1- 2], in fcc materials to examine the directional nature of twinning which cannot be explained by classical twin nucleation models or the "twinnability" criterion. By accounting for these energy pathways in a multiscale model, we quantitatively predict the critical twinning stress for the (111) [1- 1- 2] mode to be substantially higher compared to the favorable (111) [11 2-] mode (whose predicted stresses are in agreement with experiment), thus, ruling out twinning in the (111) [1- 1- 2] mode.