I have some questions about CSL (coincidence site lattice) boundaries between crystal grains. 1. What is the relation between twin boundaries and CSL boundaries? Is it true that all twin boundaries are CSL boundaries, but not vice versa? Is the energy of twin boundaries even lower that the energy of other CSL boundaries? 2. I read an article which claims that (given a certain rotation matrix) sigma values of BCC and FCC lattices are the same as the sigma values of SC lattice. Is this true? I find it hard to belive, since BCC/FCC are composed of 2/4 displaced SC lattices and the displacement probably ruins coincidence of atom positions (so I guess sigma value of BC/FCC would be two/four times greater?). 3. Is there a theory developed that could estimate the energies of the grain boundaries based on their geometry (and some easily measurable macroscopic quantities)? If so, please recommend literature.