[QE-users] elph.xml vs printed electron-phonon matrix element at Gamma (ph.x)

[Qi Sun]

Dear QE users,

I am trying to understand the relation between the electron-phonon matrix elements stored in elph.#iq.#irr.xml and the values printed by ph.x using electron_phonon='prt'.

QE version: 7.5
q-point: Gamma

>From elph.1.3.xml, I obtain:
  7.891896321880264E-03  -3.187338227203423E-16

However, the value printed by ph.x for the same Gamma point is:
  0.5937940455E-01 meV

I have checked that:
- both correspond to the Gamma point
- the same perturbation/mode is used
- the band indices are consistent

My question is:
what transformations are applied between the raw matrix elements in elph.xml and the printed values in ph.x?

Can the printed value be reconstructed directly from the XML data?

In particular, I see many k-points stored in the XML file, while the output file only provides the value of g at the Gamma point when setting kx=0, ky=0, kz=0. How should the matrix elements at other k-points be interpreted or used?

Thank you very much for your help.

Best regards,
Qi
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