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Phonon frequencies and irreducible representations 
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Joined: Tue Nov 20, 2018 10:43 am
Posts: 3
University: Uppsala University
Post Phonon frequencies and irreducible representations
Dear All,

I am trying to compute the electron-phonon coupling matrix for an 8 atom cell using ph.x with k-grid of 12x12x6 and q-point 4x4x2.

I am computing each of the 12 q-points separately. For the first q-point (gamma-point), the system has 16 irreps. From the output file one can get all the mode symmetries for each irrep and corresponding frequencies, as shown below:


------------------------------------------------------------------------
Mode symmetry, D_4h(4/mmm) point group:


Atomic displacements:
There are 16 irreducible representations

Representation 1 1 modes -A_1g X_1 M_1 Done

Representation 2 1 modes -A_1g X_1 M_1 Done

Representation 3 1 modes -B_1g X_2 M_2 Done

Representation 4 1 modes -B_1g X_2 M_2 Done

Representation 5 2 modes -E_g X_5 M_5 Done

Representation 6 2 modes -E_g X_5 M_5 Done

Representation 7 2 modes -E_g X_5 M_5 Done

Representation 8 2 modes -E_g X_5 M_5 Done

Representation 9 1 modes -A_2u X_4' M_4' Done

Representation 10 1 modes -A_2u X_4' M_4' Done

Representation 11 1 modes -A_2u X_4' M_4' Done

Representation 12 1 modes -A_2u X_4' M_4' Done

Representation 13 2 modes -E_u X_5' M_5' Done

Representation 14 2 modes -E_u X_5' M_5' Done

Representation 15 2 modes -E_u X_5' M_5' Done

Representation 16 2 modes -E_u X_5' M_5' Done


q = ( 0.000000000 0.000000000 0.000000000 )

**************************************************************************
freq ( 1) = -0.143039 [THz] = -4.771283 [cm-1]
freq ( 2) = 0.141240 [THz] = 4.711264 [cm-1]
freq ( 3) = 0.141240 [THz] = 4.711264 [cm-1]
freq ( 4) = 1.868022 [THz] = 62.310502 [cm-1]
freq ( 5) = 1.868022 [THz] = 62.310502 [cm-1]
freq ( 6) = 2.532549 [THz] = 84.476756 [cm-1]
freq ( 7) = 3.475908 [THz] = 115.943802 [cm-1]
freq ( 8) = 3.475908 [THz] = 115.943802 [cm-1]
freq ( 9) = 4.146052 [THz] = 138.297422 [cm-1]
freq ( 10) = 4.146052 [THz] = 138.297422 [cm-1]
freq ( 11) = 5.200291 [THz] = 173.463047 [cm-1]
freq ( 12) = 5.934808 [THz] = 197.963889 [cm-1]
freq ( 13) = 6.503338 [THz] = 216.928000 [cm-1]
freq ( 14) = 7.792651 [THz] = 259.934858 [cm-1]
freq ( 15) = 8.280964 [THz] = 276.223233 [cm-1]
freq ( 16) = 8.280964 [THz] = 276.223233 [cm-1]
freq ( 17) = 8.684696 [THz] = 289.690268 [cm-1]
freq ( 18) = 8.684696 [THz] = 289.690268 [cm-1]
freq ( 19) = 10.769522 [THz] = 359.232578 [cm-1]
freq ( 20) = 11.594174 [THz] = 386.740014 [cm-1]
freq ( 21) = 11.594174 [THz] = 386.740014 [cm-1]
freq ( 22) = 15.172169 [THz] = 506.089090 [cm-1]
freq ( 23) = 16.389027 [THz] = 546.679088 [cm-1]
freq ( 24) = 16.389027 [THz] = 546.679088 [cm-1]
**************************************************************************


Mode symmetry, D_4h(4/mmm) point group:

freq ( 1 - 1) = -4.8 [cm-1] --> A_2u X_4' M_4' I
freq ( 2 - 3) = 4.7 [cm-1] --> E_u X_5' M_5' I
freq ( 4 - 5) = 62.3 [cm-1] --> E_u X_5' M_5' I
freq ( 6 - 6) = 84.5 [cm-1] --> A_2u X_4' M_4' I
freq ( 7 - 8) = 115.9 [cm-1] --> E_g X_5 M_5 R
freq ( 9 - 10) = 138.3 [cm-1] --> E_g X_5 M_5 R
freq ( 11 - 11) = 173.5 [cm-1] --> A_1g X_1 M_1 R
freq ( 12 - 12) = 198.0 [cm-1] --> A_1g X_1 M_1 R
freq ( 13 - 13) = 216.9 [cm-1] --> B_1g X_2 M_2 R
freq ( 14 - 14) = 259.9 [cm-1] --> A_2u X_4' M_4' I
freq ( 15 - 16) = 276.2 [cm-1] --> E_u X_5' M_5' I
freq ( 17 - 18) = 289.7 [cm-1] --> E_g X_5 M_5 R
freq ( 19 - 19) = 359.2 [cm-1] --> B_1g X_2 M_2 R
freq ( 20 - 21) = 386.7 [cm-1] --> E_u X_5' M_5' I
freq ( 22 - 22) = 506.1 [cm-1] --> A_2u X_4' M_4' I
freq ( 23 - 24) = 546.7 [cm-1] --> E_g X_5 M_5 R
electron-phonon interaction ...
--------------------------------------------------------------------------

By comparing the Raman modes of point groups, I can identify the corresponding frequencies and thereby elph.#iq.#irr.xml File (there are 16 elph.#iq.#irr.xml files).

The next q-point (0.000000000 0.000000000 -0.239442795) also has 16 irreps, but the Raman modes are not specified in this case;

-------------------------------------------------------------------------
Atomic displacements:
There are 16 irreducible representations

Representation 1 2 modes - Done

Representation 2 2 modes - Done

Representation 3 2 modes - Done

Representation 4 1 modes - Done

Representation 5 1 modes - Done

Representation 6 1 modes - Done

Representation 7 2 modes - Done

Representation 8 2 modes - Done

Representation 9 1 modes - Done

Representation 10 1 modes - Done

Representation 11 1 modes - Done

Representation 12 2 modes - Done

Representation 13 1 modes - Done

Representation 14 2 modes - Done

Representation 15 2 modes - Done

Representation 16 1 modes - Done

q = ( 0.000000000 0.000000000 -0.239442795 )

**************************************************************************
freq ( 1) = 1.057811 [THz] = 35.284761 [cm-1]
freq ( 2) = 1.057811 [THz] = 35.284761 [cm-1]
freq ( 3) = 1.480778 [THz] = 49.393431 [cm-1]
freq ( 4) = 1.536907 [THz] = 51.265692 [cm-1]
freq ( 5) = 1.536907 [THz] = 51.265692 [cm-1]
freq ( 6) = 2.357932 [THz] = 78.652135 [cm-1]
freq ( 7) = 3.508436 [THz] = 117.028814 [cm-1]
freq ( 8) = 3.508436 [THz] = 117.028814 [cm-1]
freq ( 9) = 4.136431 [THz] = 137.976482 [cm-1]
freq ( 10) = 4.136431 [THz] = 137.976482 [cm-1]
freq ( 11) = 5.311737 [THz] = 177.180465 [cm-1]
freq ( 12) = 5.687131 [THz] = 189.702287 [cm-1]
freq ( 13) = 6.580806 [THz] = 219.512069 [cm-1]
freq ( 14) = 7.755222 [THz] = 258.686350 [cm-1]
freq ( 15) = 8.278951 [THz] = 276.156083 [cm-1]
freq ( 16) = 8.278951 [THz] = 276.156083 [cm-1]
freq ( 17) = 8.666585 [THz] = 289.086145 [cm-1]
freq ( 18) = 8.666585 [THz] = 289.086145 [cm-1]
freq ( 19) = 10.777740 [THz] = 359.506708 [cm-1]
freq ( 20) = 11.612857 [THz] = 387.363206 [cm-1]
freq ( 21) = 11.612857 [THz] = 387.363206 [cm-1]
freq ( 22) = 15.267973 [THz] = 509.284772 [cm-1]
freq ( 23) = 16.394501 [THz] = 546.861684 [cm-1]
freq ( 24) = 16.394501 [THz] = 546.861684 [cm-1]
**************************************************************************
electron-phonon interaction ...

-------------------------------------------------------------------------

I was using the same version on the same computer. On the latter case, I can't identify the frequencies corresponding to elph.#iq.#irr.xml files. Out of 12 q-points Raman modes are specified only on 5 of them.

Please help me to solve this. Or any other method to get the frequencies corresponding to each irrep.

Thank you for your time and consideration,
Best regards,
Fairoja.
-----------
Fairoja Cheenicode Kabeer
Postdoctoral researcher,
Materials Theory,
Uppsala University,
Uppsala, Sweden.


Tue Nov 20, 2018 12:11 pm
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Joined: Wed Jan 13, 2016 7:25 pm
Posts: 532
University: Oxford
Post Re: Phonon frequencies and irreducible representations
Dear Fairoja,

It seems you are using the phonon code ph.x (i.e. not the EPW code).
Therefore such question might be best asked on the Quantum Espresso mailing list.

The expert for this should be Prof. Andrea Dal Corso.

Best wishes,
Samuel

_________________
Dr. Samuel Poncé
Department of Materials
University of Oxford
Parks Road
Oxford OX1 3PH, UK


Thu Nov 22, 2018 10:29 am
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Joined: Tue Nov 20, 2018 10:43 am
Posts: 3
University: Uppsala University
Post Re: Phonon frequencies and irreducible representations
Dear Samual,

Thank you very much for the quick reply!

Best regards,
Fairoja.


Fri Nov 23, 2018 11:35 pm
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