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discontinuities in epmatwef
http://epwforum.uk/viewtopic.php?f=3&t=744
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Author:  MaxS [ Wed Jan 09, 2019 7:43 pm ]
Post subject:  discontinuities in epmatwef

Hello EPW community,

I have plotted the absolute values of epmatwef (g in Wannier-Phonon representation) for graphene. The parameters are:
q-path: Gamma > M > K > Gamma
Re=0
ibnd=jbnd=4 (one of the two pi orbitals)

Therefore we are seeing the on-site el-ph coupling of a pi orbital in graphene, while the modes according to QE are as follows.
1, 2: acoustic in-plane longitudinal/transversal
3: acoustic out-of-plane
4, 5: optical in-plane longitudinal/transversal
6: optical out-of-plane

My question is: Why are there discontinuities e.g. between G and M for modes 3 and 4? To me it looks like the order of the modes in not preserved. I.e. the order within epmatwef does not correspond to the initial order from QE. Is that so?

Image

Author:  carla.verdi [ Wed Jan 09, 2019 11:04 pm ]
Post subject:  Re: discontinuities in epmatwef

Hi,

The order of the phonon modes at arbitrary q points, in both QE and EPW, is just of ascending phonon frequencies, that is the character of the modes is not followed. The discontinuities are therefore due to phonon crossings (e.g. looking at phonon dispersions I see modes 3 and 4 swapping along GM and KG).

Best,
Carla

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