2. For the bilayers formed from dynamically stable monolayers, we have computed the difference in total energy/atom, ∆E f -n , between the frustrated and the nonfrustrated supercells, which is given by ∆E f -n = E f /n f -E n /n n where E f , E n are the total energy of the frustrated and non-frustrated supercells, respectively, and n f and n n are the number of atoms in the frustrated and non-frustrated supercells, respectively.