Surface effect on the GSF energy of Al

The second-nearest-neighbor modified embedded atom method (2NN-MEAM) is used to calculate the generalized stacking fault (GSF) energy for (1 1 1) surface of Al crystal. It is found that the GSF energy curve is much lower for the fault in the first layer of the (1 1 1) surface than that in the bulk. When the fault exists in the second layer, the energy curve becomes considerably on the verge of that in the bulk. With a much lower unstable stacking fault energy γ_usf, the dislocation should be easier to set on at the outermost of the free surface. Expansion in relaxation always exists for the stacking fault either in bulk or near the surface and the GSF energy increases with the vertical expansion.