[Pw_forum] symmetry operation not allowed

[Stefano de Gironcoli]

Lily Anh wrote:
> Thanks for your suggestion.
> I have changed ecutwfc (from 20-50Ry every 5 Ry), ecutrho (200-1200 
> every 50), k grid. But nothing works. How to change nr1 nr2 nr3, 
> larger or smaller?
nr1, nr2 and nr3 are input parameters in the &control namelist that 
usually take a default value on the basis of ecutrho but can be 
specified directly  when needed (as in this case) .
> The structure should have 4 symmetry operations while the code can not 
> find any symmetry. I want to reduce the calculation time.
the code finds correctly all 4 symmetry operations but discards them 
(except the trivial identity) because of the incompatibility of the 
required fractional translation with the FFT grid. By choosing a 
different origin for your system it could be possible to make the 
fractional translations simple  fractions of the fundamental lattice 
vectors.

Hope it helps,
   stefano