[Pw_forum] Fourier interpolation for DFPT

[Dragoni Daniele]

Dear Krishnendu,


in order to perform the so-called Fourier-interpolation you need first to compute phonon frequencies with DPTF on a proper grid of q-points using ph.x. From the dynamical matrix produced by the phonon code you can then compute the interatomic force constants (IFC) in real space using the q2r.x code. From there, it is possible to recompute the phonon frequencies at any arbitrary q-point by means of the matdyn.x code. At this stage, you can specify the q-mesh (or a list of specific q-points) that is required for calculating converged values of the quantities you are interested in (in our case a 21x21x21 mesh was sufficient). For more specific information, try to have a look at this very useful document by Paolo Giannozzi  http://www.fisica.uniud.it/~giannozz/QE-Tutorial/tutorial_disp.html


Both q2r.x and matdyn.x should be automatically compiled by typing "make ph" from the main quantum Espresso directory, as stated (for example) here http://www.afs.enea.it/software/qu_esp/Doc/ph_6.0.0.pdf


Examples of q2r and matdyn input files can be found here

http://www.fisica.uniud.it/~giannozz/QE-Tutorial/examples_disp.tgz

Have also a look at this tutorial (Exercise 2 in particular)

http://www.tcl.t.u-tokyo.ac.jp/pdf/2014_lm/3rd_day_pm.pdf


In particular you can read:

##q2r input template

&INPUT
    fildyn = ***,
    flfrc  = ***,
    zasr   = ***,    (we use crystal)
 /

##


## matdyn input template

&INPUT
    ntyp  = ***,    (we have 1 atom type)
    flvec = ***,
    flfrc = ***,
    asr   = ***,    (we use crystal)
    amass(1) = ***,
/
***               (integer # of q points for which you want compute phonon frequencies)
x1 x2 x3  0 (here goes a list of q points coordinates followed by a growing integer number N counting the q-points. In our case, this list should correspond to a 21x21x21 MP grid)

x1 x2 x3  1
x1 x2 x3  2

...

...

##

Replace *** with the correct input card. An exhaustive description of the input cards available for the two codes can be found in the header of the source codes q2r.f90 and matdyn.f90 in /yourQEfolder/PHonon/PH directory.


Hope this helps!

Best regards,

   Daniele

__________________________________________

Daniele Francesco Dragoni
Laboratoire de théorie et simulation des matériaux
Swiss Federal Institute of Technology
EPFL STI IMX THEOS
ME D2 1020
Station 9
CH-1015, Lausanne
+41 21 69 31956
<tel:+41216931956>

________________________________
From: pw_forum-bounces at pwscf.org <pw_forum-bounces at pwscf.org> on behalf of Krishnendu Mukherjee <krishnendu.mukherjee789 at gmail.com>
Sent: Tuesday, January 2, 2018 10:31 AM
To: pw_forum at pwscf.org
Subject: [Pw_forum] Fourier interpolation for DFPT


Dear experts,

 I am interested in calculating the phonon calculation of bcc iron ferrite. I am following the article titled "Thermoelastic properties of alpha-iron from first-principles" authored by Daniele Dragoni, Davide Ceresoli and Nicola Marzari, published in PRB 91, 104105. In that article it is mentioned that,

"Phonon calculations were carried out for each deformation within DFPT. The dynamical matrix and its eigenvalues are calculated on an 4x4x4 mesh of special points in the BZ and Fourier-interpolated on an extended 21x21x21 grid for integration of thermodynamic quantities."

 Now I gave the nq1=4, nq2=4, nq3=4 at fe.ph.in<http://fe.ph.in> according to the values mentioned in the article.

 But I do not know the parameter for which I have to set the values 21x21x21. Can you kindly let me know the parameter where I have to put the values to set the Fourier-interpolation extension grid for integration of thermodynamic quantities.

Thanking you,
Yours sincerely,
Krishnendu

--
Dr. Krishnendu Mukherjee,

Principal Scientist,
CSIR-NML,
Jamshedpur.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20180105/45738308/attachment.html>