[Pw_forum] NRAPP not giving phonon frequencies

[Lorenzo Paulatto]

Quoting Bipul Rakshit <bipulrr at gmail.com>:
> One more thing I want to ask is that, after computing first 3 modes using
> nrapp, where do i find the dynamical matrix? Because in LaMnO3.dyn2 file is
> empty, after the calculation is finished.
>
> Is the non-diagonalised matrix is printed elsewhere?

It is printed in output, or at least that's what I've got after doing  
some single-mode calculation:
      Dynamical matrix:
          1    1 -0.276205  0.000000
          1    2 -0.000065  0.000000
          1    3  0.071921  0.000000
          1    4 -0.102158  0.000000
          [...]

Which means M_{13} = 0.071921 + i 0.000000

Although, that happens when you use modenum=# in the input. Now that  
you made me recall it, I think that by using nrapp+list of  
representations you don't get the dynamical matrix line.

You can just rerun the code with modeunm=1, 2 and 3 (three separate  
runs) and it will pop you the line in a few minutes (they are already  
computed, just not printed). You can also extract them by hand from file
   $otudir/_php$prefix.save/data-file.xml.1.$R
where $R is the representation number.

If your system has symmetry, this may not be correct. I think it is,  
but I am quite confused by the differences (if any) between nrapp,  
nat_todo, modenum and/or start_irr+last_irr. I would rather refrain  
from further comment than tell you something wrong.

-- 
Lorenzo Paulatto
SISSA & DEMOCRITOS


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