[Pw_forum] Electron-phonon matrix calculation and elph.#iq.#irr.xml

Jaehong Park ignasio.ssp at gmail.com
Mon May 11 05:15:51 CEST 2015

Dear Quantum-ESPRESSO,

I am trying to calculate phonon related property of 2-dimensional
transition metal dichalcogenide(TMDC) and i have several questions about
electron-phonon matrix calculation;

elphmat(j,i) = <psi_{k+q,j}|dvscf_q*psi_{k,i}>

in code "elphon.f90"

>From developer manual and source code of ph.x, I found that the
electron-phonon matrix is written in the file "elph.#iq.#irr.xml" in
q-point and irrep(irreducible representation) wise manner.

There are three questions.


Since my unitcell(2-D TMDC monolayer slab with vacuum) has one metal atom
and two surfur atoms, there are 9 normal modes in total.

At gamma point(q-point), there are only 6 irreps and thus 6 elph.1.#irr.xml
files where #irr runs from 1 to 6 due to degeneracy,

However, where q-point!=0 without such degeneracy, there are 9 irreps and
corresponding 9  elph.#iq.#irr.xml  files.

So, i cannot figure out how i can get collection of xml files which
correspond to the specific normal mode i concern for all q-points(by
collecting xml files for q=0 and q!=0).

Numbering  each mode or irrep even does not seem to follow magnitude of the
phonon frequency. I also looked into relevant ph.x source codes but i
couldn't understand.


I want to know which physical quantity the values in elph.#iq.#irr.xml
stand for.

The developer manual of ph.x reads;

"elph.#iq.#irr.xml contains the contribution to the electron phonon
coefficients at the q vector #iq of the representation #irr. These files
are written by elphel and contain the quantities g_qν (k, i, j) (see User

and  g_qν (k, i, j) seems to contain factor "sqrt[h/(2*M*w)]" followed by

from User Manual.

But, i found that the values of g_qν (k, i, j) in elph.#iq.#irr.xml do not
change with mass of atoms (To check this, i artificially change mass of
surfur atoms to 100000)

I also, wondering the value in elph.#iq.#irr.xml  are whether

<\psi(k+q)|dV_{SCF}/du^q_{i a}|\psi(k)>   (which is written in elphon.f90)

or just,



It seems little trivial, I want to know some detail inside the

Following is my elph.1.1.xml


    <NUMBER_OF_BANDS type="integer" size="1">
      <COORDINATES_XK type="real" size="3" columns="3">
 0.000000000000000E+000  0.000000000000000E+000  0.000000000000000E+000
      <PARTIAL_ELPH type="complex" size="289">
 8.430451497377110E-012, 1.448582735931787E-011
 3.014026080010312E-002, 7.108929268140980E-010



The lines after <PARTIAL_ELPH type="complex" size="289"> would be

the g_qν (k, i, j) for q=gamma, v=1 (first irrep) and k=gamma.

I guess that, since the total number of electronic bands are 17, 17x17
lines after  <PARTIAL_ELPH type="complex" size="289"> are

g values in following order

band-i (initial band), band-j (final band)

is it true?

Finally,  the values of second column for each line seem to be imaginary
part of g. I am not good at quantum mechanics but i thought perturbing
hamiltonian by phonon should be also hermitian and 'diagonal' element
should be real number.
But in this case, there are so many indices g(q,v,i,j,k) that i cannot
figure out what is 'diagonal' element of g in this case.

I apologize for ill-organized questions.

Thank you in advance.

Best regards

Jaehong Park

Jaehong Park
Ph.D. Candidate
Dielectric Thin Film Laboratory
Department of Materials Science & Engineering , Seoul National University

Electronic Materials Research Center

Post-Si Semiconductor Institute

Korea Institute of Science and Technology (KIST)
Hwarangno 14-gil, Seongbuk-gu, Seoul, 136-791, KOREA

Tel :      +82-2-958-6653

Mobile : +82-10-5481-5143

E-mail : catinabox at snu.ac.kr
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20150511/62f00ed5/attachment.html>

More information about the users mailing list