Dear Manoj, I do not know about the definitions intrinsic to pwscf, but in group theory directed opperations are not allways equivalent. In this case, the rotations about -z and z will be inequivalent if there is no opperation of the group which reverses the sense of the z axis.
For example, in the T group there are 8 C3 opperations although there are only four cube diagonals- see Tinkham "Group Theory and Quantum mechanics" 2003 pp 58. Alexandra Carvalho EPFL Lausanne Quoting Manoj Srivastava <manoj at phys.ufl.edu>: > Dear PWSCF users and developers, > I was looking into the code where it calculates symmerty operations for > the group. Now the symmetry operations are defined as ' 90 deg rotation - > cart. axis [0,0,-1]', & ' 90 deg rotation - cart. axis [0,0,1] > I did not understand the point of defining rotation about z and -z > axis. Is this because of some numerical constraint? Also, there are > elements with 'theta' and '-theta' rotation in the same group. I was just > wondering the reason behind this. Any help will be appreciated. > > Regards, > Manoj Srivastava > Department of Physics > University of Florida > Gainesville, FL, USA. > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum >
