[Pw_forum] Electron-phonon matrix calculation and elph.#iq.#irr.xml
Jaehong Park
ignasio.ssp at gmail.com
Wed May 20 13:25:57 CEST 2015
Dear Paolo;
Thank you very much for your answer
However, it is difficult for me to understand your answer. Can you be more
specific?
For example, singularity of acoustic phonon at gamma and zero
coefficient...
and to make my original question more specific,
following is my output of ph.x
at Gamma point (q=0)
-----------------------------------------------------------------------------------------------
Mode symmetry, D_3h (-62m) point group:
Atomic displacements:
There are 6 irreducible representations
Representation 1 1 modes -A'_1 To be done
Representation 2 2 modes -E' To be done
Representation 3 2 modes -E' To be done
Representation 4 1 modes -A''2 To be done
Representation 5 1 modes -A''2 To be done
Representation 6 2 modes -E'' To be done
...
...
Diagonalizing the dynamical matrix
q = ( 0.000000000 0.000000000 0.000000000 )
**************************************************************************
freq ( 1) = -0.266351 [THz] = -8.884502 [cm-1]
freq ( 2) = 0.470018 [THz] = 15.678118 [cm-1]
freq ( 3) = 0.470018 [THz] = 15.678119 [cm-1]
freq ( 4) = 8.700163 [THz] = 290.206203 [cm-1]
freq ( 5) = 8.700164 [THz] = 290.206217 [cm-1]
freq ( 6) = 11.760562 [THz] = 392.290107 [cm-1]
freq ( 7) = 11.760562 [THz] = 392.290126 [cm-1]
freq ( 8) = 12.300285 [THz] = 410.293340 [cm-1]
freq ( 9) = 14.310518 [THz] = 477.347485 [cm-1]
**************************************************************************
Mode symmetry, D_3h (-62m) point group:
freq ( 1 - 1) = -8.9 [cm-1] --> A''2 I
freq ( 2 - 3) = 15.7 [cm-1] --> E' I+R
freq ( 4 - 5) = 290.2 [cm-1] --> E'' R
freq ( 6 - 7) = 392.3 [cm-1] --> E' I+R
freq ( 8 - 8) = 410.3 [cm-1] --> A'_1 R
freq ( 9 - 9) = 477.3 [cm-1] --> A''2 I
----------------------------------------------------------------------------------------------------
At the gamma point as you can see from above, two dimensional irrep, E',
appears twice as "Representation 2" and "Representation 3".
and i get elph.1.2.xml , elph.1.3.xml for them, which may be printed in
order according to elphon.f90 code ( i am interested in extracting
electron-phonon matrix element).
but the two irrep E' are definitely inequivalent (different freq.) and i
do not know whether the frequency of "Representation 2" is "15.7" or
"392.3".
This problem makes me hard to identify elph.1.2.xml and elph.1.3.xml since
i cannot assign the frequency.
This problem becomes even worse when the site symmetry of q-point is reduced
q = ( 0.000000000 0.128300065 0.000000000 )
-------------------------------------------------------------------------------------------
Mode symmetry, C_2v (mm2) point group:
Atomic displacements:
There are 9 irreducible representations
Representation 1 1 modes -A_1 D_1 S_1 To be done
Representation 2 1 modes -A_1 D_1 S_1 To be done
Representation 3 1 modes -A_1 D_1 S_1 To be done
Representation 4 1 modes -A_2 D_2 S_2 To be done
Representation 5 1 modes -B_1 D_3 S_3 To be done
Representation 6 1 modes -B_1 D_3 S_3 To be done
Representation 7 1 modes -B_2 D_4 S_4 To be done
Representation 8 1 modes -B_2 D_4 S_4 To be done
Representation 9 1 modes -B_2 D_4 S_4 To be done
...
...
...
Mode symmetry, C_2v (mm2) point group:
freq ( 1 - 1) = 11.2 [cm-1] --> B_2 D_4 S_4
freq ( 2 - 2) = 56.2 [cm-1] --> B_1 D_3 S_3
freq ( 3 - 3) = 90.1 [cm-1] --> A_1 D_1 S_1
freq ( 4 - 4) = 292.5 [cm-1] --> A_2 D_2 S_2
freq ( 5 - 5) = 300.9 [cm-1] --> B_2 D_4 S_4
freq ( 6 - 6) = 385.3 [cm-1] --> A_1 D_1 S_1
freq ( 7 - 7) = 390.9 [cm-1] --> B_1 D_3 S_3
freq ( 8 - 8) = 414.1 [cm-1] --> A_1 D_1 S_1
freq ( 9 - 9) = 466.7 [cm-1] --> B_2 D_4 S_4
--------------------------------------------------------------------------------------------
As you can see, irrep A_1 appears triply.
How can i resolve this problem ?
(I found similar thread in pw_forum
http://qe-forge.org/pipermail/pw_forum/2009-March/086475.html
but i couldn't find solution.)
Thank you in advance.
Best regards
Jaehong Park
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