Theoretical strength and charge redistribution of fcc Ni in tension and shear

We employ a first-principles total-energy method to investigate the theoretical tensile and shear strengths of fcc Ni systematically. The theoretical tensile strengths are shown to be 36.1, 10.5 and 34.1 GPa in the [001], [110] and [111] directions, respectively. We indicate that [110] is the weakest direction due to the formation of an instable bct 'phase' in the tensile process. The theoretical shear strengths are, respectively, 5.1 and 15.8 GPa in the 'easy' and 'hard' directions in the slip system, and 6.4 GPa in the slip system. Both the tensile and the shear strengths are consistent with either experimental or theoretical values. The different shear strengths in the 'easy' and 'hard' directions originate from the different charge redistribution under the shear strain. The shear strain along the 'easy' direction of [112] results in a charge distributed in the which forms a directional bond, while the strain along the 'hard' direction of [112] makes the charge extend to the whole {111} interlayers.