[Pw_forum] Weird jump in phonon dispersion at Gamma point
Dear Eduarodo and Lorenzo, Thank you very much for your explanation. That make sense to me. Lorenzo, probably you mean another thread? I failed to find your post in the discussion I linked in my initial post. Regards, Yao -- Yao Yao PhD. Candidate 3rd Generation Strand ARC Photovoltaics Centre of Excellence University of New South Wales Sydney, NSW Australia -- next part -- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20121110/d0b671ac/attachment.html
[Pw_forum] Weird jump in phonon dispersion at Gamma point
Yes, it was another thread: < http://pwscf.org/pipermail/pw_forum/2012-October/099881.html> (please note that the mailing list archive has moved since october 4th). I'm happy you could sort it out -- Dr. Lorenzo Paulatto IdR @ IMPMC -- CNRS & Universit? Paris 6 phone: +33 (0)1 44275 084 / skype: paulatz www: http://www-int.impmc.upmc.fr/~paulatto/ mail: 23-24/4?16 Bo?te courrier 115, 4 place Jussieu 75252 Paris C?dex 05 -- next part -- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20121110/6b224fe8/attachment.html
[Pw_forum] Weird jump in phonon dispersion at Gamma point
Dear Yao,
The jumps probably are right. They appear in non-cubic systems. For very
very small wavevectors, when w_TO ~ cq (c the speed of light and q the
wavavector) , the phonon are coupled with photons and form the excitation
known as phonon-polariton (PP). When the PP equations are solved the jumps
dissapear. Quantum ESPRESSO only computes the phonons, and the LO-TO
splitting is what happens for wavevectors just larger than the region of
coupling. This topics is briefly explained in some Solid State Physics
books, and fully explained in this article
R. Loudon, Advances in Physics, 2001, Vol. 50, No. 7, 813-864
There is also a short entry in Wikipedia
http://en.wikipedia.org/wiki/Polariton
Best regards,
Eduardo
Eduardo Menendez Proupin
Departamento de Qu?mica Fisica Aplicada
Facultad de Ciencias
Universidad Aut?noma de Madrid
28049 Madrid, Spain
Phone: +34 91 497 6706
On leave from: Departamento de Fisica, Facultad de Ciencias, Universidad de
Chile URL: http://fisica.ciencias.uchile.cl/~emenendez
- Mensaje reenviado --
From: Yao Yao
To:
Cc:
Date: Fri, 9 Nov 2012 11:14:39 +1100
Subject: [Pw_forum] Weird jump in phonon dispersion at Gamma point
Dear All,
I calculated a orthorhombic cell with alternating AlSb/InAs mono {110} atom
layers with QE 4.3.2. I noticed that my phonon dispersion results were with
steps at Gamma point for some optical branches. Looks you will get different
frequency at Gamma when you approach Gamma from different direction
(X->Gamma,
Y->Gamma and Z->Gamma). One picture showing this is uploaded to
http://www.picvalley.net/v.php?p=u/2753/176658145760478725413524194617CoVRtxOq5iqZ20Wa3iK.PNG
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[Pw_forum] Weird jump in phonon dispersion at Gamma point
Dear All,
I calculated a orthorhombic cell with alternating AlSb/InAs mono {110} atom
layers with QE 4.3.2. I noticed that my phonon dispersion results were with
steps at Gamma point for some optical branches. Looks you will get different
frequency at Gamma when you approach Gamma from different direction (X->Gamma,
Y->Gamma and Z->Gamma). One picture showing this is uploaded to
http://www.picvalley.net/v.php?p=u/2753/176658145760478725413524194617CoVRtxOq5iqZ20Wa3iK.PNG
Looks this is similar to the problem reported here
http://www.democritos.it/pipermail/pw_forum/2009-June/013250.html
But seems that problem has been solved according to the following email. Is
this another problem in q2r or matdyn?
The cell was optimised to
ATOMIC_POSITIONS alat
Al -0.025264682 0.0 0.0
In 0.700737593 0.479363399 0.476965330
Sb 0.322108083 0.479363399 0.0
As 1.029274264 0.0 0.476965330
CELL_PARAMETERS
1.351237 0.00 0.00
0.00 0.958727 0.00
0.00 0.00 0.953931
Thank you very much.
Regards,
Yao
[Pw_forum] Weird jump in phonon dispersion at Gamma point
On 9 November 2012 01:14, Yao Yao wrote: > Looks this is similar to the problem reported here > http://www.democritos.it/pipermail/pw_forum/2009-June/013250.html > But seems that problem has been solved according to the following email. Is > this another problem in q2r or matdyn? > > As I stated several times in the discussion that you are linking, those "weird jumps" are *an actual physical phenomenon*. If you remove them *you are doing it wrong*! The problem is not with the code, but your understanding of the problem. I do not want to be rude, this is just to * warn* you that you may be going in the wrong direction. Anyway: * if you have understood that LO-TO splitting is induced by the long range interaction of effective charges in polar insulators/semiconductors * if you still think that removing this splitting is the right thing to do * if you promise to *not* cite me as the source of this information then, edit PH/matdyn.f90 and around line 466 replace ELSE lo_to_split=.TRUE. ENDIF ! CALL nonanal (nat, nat_blk, itau_blk, epsil, qhat, zeu, omega, dyn) with ELSE lo_to_split=.FALSE. ENDIF ! !!! CALL nonanal (nat, nat_blk, itau_blk, epsil, qhat, zeu, omega, dyn) i.e. set lo_to_split to .false. in every case and do not compute the non-analitical long-range term. Then recompile the phonon code best regards -- Dr. Lorenzo Paulatto IdR @ IMPMC -- CNRS & Universit? Paris 6 phone: +33 (0)1 44275 084 / skype: paulatz www: http://www-int.impmc.upmc.fr/~paulatto/ mail: 23-24/4?16 Bo?te courrier 115, 4 place Jussieu 75252 Paris C?dex 05 -- next part -- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20121109/93808b4e/attachment.html
