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I've generated a phonon dispersion for BCC lithium using the python api for phonopy. I specified the following q-point path

path = [[[0.0, 0, 1.0], [0.5, 0.5, 0.5],[0, 0, 0], [0.0, 0.25, 0.25]]] 

and then run

phonon.run_band_structure(qpoints, path_connections=connections, labels=labels)

After using the utility

phonopy-bandplot  --gnuplot band.yaml

I obtain a .plot file for comparison with a QE phonon dispersion. I noticed that I had to scale the phonopy q-vector axis a factor equal to the lattice paramter to match the two up. However, even doing this, I find that the phonopy dispersion abruptly ends before the final q-point segment has completed. I wondered if anyone has tried to do this before and knows how to correctly compare the two?

P.S. The q-point path I specify in QE is

   5
  0.00000000 0.00000000 0.0   40
  0.0 0.0 1.0   40
  0.5 0.5 0.5   40
  0.00000000 0.00000000 0.0   40
  0.0        0.5    0.5   1

Directly translating this into the phonopy path

path = [[[0, 0, 0], [0.0, 0, 1.0], [0.5, 0.5, 0.5],[0, 0, 0], [0.0, 0.5, 0.5]]]

gives totally different results (as if extra segments have been added to the path). I think I'm misunderstanding how phonopy creates its band paths.

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  • $\begingroup$ Actually, I think I solved the problem. I had to use the path path = [[[0, 0, 0], [-0.5, 0.5, 0.5], [0.25, 0.25, 0.25],[0, 0, 0], [0.0, 0.5, 0.0]]] even although I specified that my lattice vectors should be [[-0.5,0.5,0.5],[0.5,-0.5,0.5],[0.5,0.5,-0.5]] (the path would ostensibly correspond to the choice of lattice vectors [[0.5,0.5,-0.5],[-0.5,0.5,0.5],[0.5,-0.5,0.5]] but maybe phonopy does something under the hood that I'm not aware of) . Seems strange but figured I'd leave this here in case it's helpful to anyone else. $\endgroup$ Commented Oct 29, 2023 at 9:08

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