[Pw_forum] improper symmetry analysis

[Lorenzo Paulatto]

22 aprile 2009 alle ore 09:33:32, Kun Yin <kyin.cn at gmail.com> ha scritto:
>  I think this missing of symmetries will not affect calculation of groud
> state energy. But if I use this scf calculation results to do phonon
> calculations, can I get correct phonon band assignment?

Dear Kun Yin,
just manually specify the dimension of the FFT grid along the direction  
where the symmetry operation is lost, it is printed in output in this form:
      G cutoff =   84.7099  (  32329 G-vectors)     FFT grid: ( 20, 20,216)
or, if you have, ecutrho > 4*ecutwfc in the following form:
      G cutoff =  677.6793  ( 365691 G-vectors)     FFT grid: ( 54, 54,300)
      G cutoff =  338.8396  ( 129571 G-vectors)  smooth grid: ( 40, 40,216)
just make sure that the dimensions of the grids are multiple of the  
numbers of replicas in the fractional traslation.

Where they are not, you can specify them manually using the  
system-namelist keywords nr1, nr2 and nr3 for the FFT grid; and nr1s, nr2s  
and nr3s for the smooth grid. You should not decrease them from their  
default value, but only increase them!

regards


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Lorenzo Paulatto
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