[Pw_forum] dipole correction and slab phonon

[秦新明]

Dear all
  I got a serious problem when using QE to apply dipole corrections in the phonon calculation for a slab with a large dipole moment. I perform the phonon calculations with and without the dipole correction. And I find that the corresponding phonons are very different. When the dipole correction is applied, two acoustic branches are imaginary at high frequencies. However, without the dipole correction, all frequencies are positive and the phonon dispersion is similar with the reslut form the frezon-phonon calculction.  Can the dipole correction be neglected ?
  Furthermore, both pw.x and ph.x do not support the symmetry when appling the dipole correction. Then a large number of k or q points are required in practical calculations. Can ph.x calcuclate phonons well with the dipole correction ?
  I'm thirsty for your reply. Thanks!
 
  Best regards

  Xinming
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