[Pw_forum] occupation problem when system changes from insulator to metal

W. YU yuwen_66 at yahoo.com
Tue Dec 14 10:22:18 CET 2004

Dear sbraccia carlo,

Thank you very much for your reply and detailed
explanations. I am now calculating the Cu3N phonon
dispersions. It is of ABO3 perovskite structure with
the A site empty. It is generally believed that under
pressure, one of the M point phonon mode corresponding
to the rotation of the BO6 octahedra will soften. I
got the same result without smearing. But when I
include smearing, the results are different. The
phonon freqencies at the same k points become much
smaller(several tens of wave numbers), and softening
happens not only at M point but also along Delta axis.
This is intuitively not correct. Which one should I

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