[Pw_forum] pseudopotential in phonon calculation

[Ruijuan Xiao]

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