On Thu, 2013-04-18 at 15:30 -0400, David Strubbe wrote: > Why are symmetries with fractional translations disabled > in supercells?
because there is no simple way to ensure that a group of point symmetries: rotations + fractional translations, is a group in the mathematical sense of the term. In a true cell, with no additional underlying translational symmetry, fractional translation are well-defined, while in a supercell there are several possible choices, differing for a lattice translation of the underlying cell. Years ago I didn't find a simple way to ensure that the choice of fractional translation was consistent with the properties of a symmetry group (if it isn't, the symmetrization procedure breaks down). Given the limited interest of this specific case, I haven't inquired any further. P. -- Paolo Giannozzi, Dept. Chemistry&Physics&Environment, Univ. Udine, via delle Scienze 208, 33100 Udine, Italy Phone +39-0432-558216, fax +39-0432-558222
