[Pw_forum] Frequency and zero point energy calculations

[Eyvaz Isaev]

Dear Lihui,

> performing calulation of frequency and zero point
> energy of CO2 molecule. However, unfortunately, I have
> obtained negative frequency.

> there are several possible reseaons: 

Well, you did not include one more reason counting them: 
there is a physical reason for this as you consider  CO2 molecule (the linear chain). Obviously, its physical properties do not change if you rotate it fixing C atom in the cell center. This might lead to negative frequencies. 

If you like to consider CO2 as a molecule you should use the Gamma point only (i.e. you consider CO2 in a big box).

> In addition, I intend to calculate the zero point
> energy of system by PHNONS code, but it does not give the
> zero point energy and other thermodynamics properties in
> output file. How could I do? I need your help
> urgently.

PH code itself does not calculate these properties. 
You can try download the QHA code from qe-forge.org. If some troubles with this, please let me know.

>  I need your help urgently.
Please keep in mind our forum consists of volunteers and nobody is oblidged to give you urgent reply.


Bests,
Eyvaz. 
P.S. Can you please show eigendisplacements? 

-------------------------------------------------------------------
Prof. Eyvaz Isaev, 
Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden 
Condensed Matter Theory Group, Uppsala University, Sweden 
Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com