Semi-empirical potentials were used to study model grain boundaries which contained numbers of atoms that ranged from a few thousand to over one hundred thousand. In boundaries of  = 3 and almost  = 3 type, in which the boundary plane was steeply inclined with respect to (111), various polytype structures appeared (such as the 9R structure). The boundaries were 1 to 2nm thick. The atomic structures, as well as micro-scale faceting, were explained in terms of the low stacking fault energy of Cu.

M.W.Finnis: Materials Science Forum, 1996, 207-209, 35-46