[Pw_forum] phonon at Gamma

[Miguel Martínez Canales]

Hi Ezad,

Ezad Shojaee escribió:
> hi
> calculating phonons at gamma for my case, i have some frequencies minus 
> and far from experimental data. there is no doubt in the structure and 
> these are my input parameters
> 
> ecutwfc=200
> ecutrho=1600
> K_points {automatic}
> 12  12  6   0 0 0
> 
> and the calculation is in the GGA approximation
> what have i missed?
> thanx for any help

You might increase the k-point sampling to see if you have hit convergence. 
  When q->gamma, acoustic modes need an increasingly large k-point grid to 
get good results. When one calculates the phonons via C(q) and C(r), this 
is usually  overcome by forcing the acoustic sum rule.

-- 
----------------------------------------
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
----------------------------------------

  "The problem with Renault is that they dont have
  the skills to convince FIA that the mass damper
  is just a brake cooler."

Annonymous