[Pw_forum] pseudopotential in phonon calculation

[Guido Roma]

Hello, 

I would say that, more than from the pseudopotential itself, the
difference comes from the exchange correlation functional (gradient
corrected PBE versus LDA) for which the pseudopotential has been
generated; by the way, you have probably different equilibrium lattice
parameters: which one is closer to the experimental value? And bulk
modulus? 
And keep in mind that conergence parameters (wfc and rho cutoff) are not
necessarily the same.

Guido
 

On Fri, 2005-07-08 at 11:35, Ruijuan Xiao wrote:
> Dear users,
> 
> I have a question about how to choose the pseudopotential correctly in the phonon calculation.Because I found that different pseudopotentials influence the results greatly. There are three kinds of elements in the system I studied. Fisrt, I use the ultrasoft pseudopotetials:Na.pbe-n-van.UPF,Co.pbe-nd-rrkjus.UPF and O.pbe-rrkjus.UPF. Almost all the freqencies I got are less than 600cm-1(the maximum is 600.31cm-1). Then I changed to use Norm-Conserving pseudopotential:Na.pz-n-vbc.UPF and O.pz-mt.UPF. Co.pz-nd-rrkjus.UPF is used for the potential of Co,because there is no Norm-Conserving pseudopotential of Co in the pseudopotential download page. And all the other parameters are same with the first calculation. But I got a very different results in the second calculation: the maximum freqence is 703.89cm-1, and it seems that all the frenqencies are enlarged especially for the high freqencies. I am puzzled why the difference is so large? Then how to choose a suitable potential!
  in
>   the calculation? Would you like to give me any information about that?
> 
> Thank you very much!
>    
> 
> 
> Best regards,                                                 
> 
> Sincerely,
> Ruijuan Xiao
> 
> 
> 
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-- 
Guido Roma <roma${at}cea.fr> -- CEA-Saclay - DEN/DMN/SRMP Bat.520/130
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