[Pw_forum] pseudopotential in phonon calculation

[Ruijuan Xiao]

Dear Guido,

Thank you very much. I forgot to mention that I use the wfc and rho cutoff as 30Ry and 300Ry in the fisrt calculation since "for a reasonable ultrasoft psp should be between 25 and 30 Ry, and unlikely to be more than 40 Ry".In the second calculation, I use the wfc and rho cutoff as 50Ry and 500Ry. The freqencies are calculated at Gamma point.I use the same lattice parameters in the two calculations, and fix the lattice parameter, then optimize the positions of atoms. I do the calculation to compare with the results of Li (Physical Review B,70,144518). I found that none results of mine is similar with his.

I agree with you that the difference has some relationship to the GGA or LDA. Do you mean that we should judge which potential is more suitable by comparing the results with experiments?

Best regards,

Sincerely,
Ruijuan Xiao