[Pw_forum] Na phonon issues

[Miguel Martínez Canales]

Nicola Marzari escribió:
> Dear Miguel,
> 
> search the archives, for negative phonon .

Dear Nicola,

thanks for your advice. I've been reading this, as well as the 
troubleshooting part of the manual. Please note that I am *not* talking 
about \Gamma. I have, then, increased the K_POINTS to 30 30 30, which seems 
pretty dense to me, unless I were to do electron-phonon calculations. This 
still yields the following omegas:
      omega( 1) =      -0.102074 [THz] =      -3.404853 [cm-1]
      omega( 2) =       0.766422 [THz] =      25.565257 [cm-1]
      omega( 3) =       1.200480 [THz] =      40.043969 [cm-1]

These aren't really that different from the ones I got with a 20 20 20 grid 
(although the longitudinal mode is 2.5% higher). Just in case, I'm running 
the script with an increased degauss value, because it's a bit too small.

The thing is, the pseudopotential is norm-conserving (or so it says on the 
header), and thus it's not an issue of not setting ecutrho. And the 
positive values are close to the numbers I get with the other pseudos. I am 
also reading the correct file, as I delete the temporary dir at the 
beginning and the end of my script. Am I being to harsh or lenient with the 
phonon threshold?

Thanks again for your comments,

Miguel

-- 
----------------------------------------
Miguel Martínez Canales
Dto. Física de la Materia Condensada
UPV/EHU
Facultad de Ciencia y Tecnología
Apdo. 644
48080 Bilbao (Spain)
Fax:  +34 94 601 3500
Tlf:  +34 94 601 5437
----------------------------------------

  "If you have an apple and I have an apple and
  we exchange these apples then you and I will
  still each have one apple. But if you have an
  idea and I have an idea and we exchange these
  ideas, then each of us will have two ideas."

    George Bernard Shaw