[Pw_forum] symmetry operations in PW

[Manoj Srivastava]

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.