0.3truein It should be noted that due to the use of periodic boundary conditions in the x- and z- directions, formation of free surfaces along the grain boundary interface is excluded in the simulation. In order to understand the effect of this assumption, and also to explore the possibility of grain boundary cleavage and formation of voids during GBS, free surface energy of (hkl) boundary plane in several structures was calculated and compared with the maximum grain boundary energy peak during GBS. The results are given in Table 1. The surface energy of the grain boundary plane (x-z plane) is computed using molecular statics simulation of a bulk crystal with periodic boundary conditions in x- and z- directions but free surfaces in y-direction. Table 1 lists twice of the magnitude of the free surface energy, since any cleavage of the interface consists of two free surfaces. It is seen that even the maximum grain boundary energy value during GBS in each boundary is significantly lower than the surface energies. This observation leads to the conclusion that boundary cleavage (or void formation) is energetically less favorable to occur compared to GBS at very low temperature.