Atomistic simulation of the vacancy in W(0 0 1) surface

The formation energies, the intra- and inter-layer migration and diffuse activation energies of a single vacancy in W(0 0 1) surface have been investigated with the modified analytical embedded-atom method (MAEAM). The results show that the effect of the surface on the vacancy is only down to the fourth-layer. It is easier for a vacancy to form and to migrate in the first layer. For inter-layer migration, a single vacancy in the second atomic layer is favorable to migrate to the first layer via the 1NN jump, that in the third atomic layer is favorable to migrate to the first layer via the 2NN jump, and that in the fourth atomic layer is favorable to migrate to the second layer via the 2NN jump. However, a single vacancy in the fifth or sixth layer is not easy to migrate to the upper layer due to its slightly higher migration energy than that of the vacancy migrating to lower layer.