# [Pw_forum] why K-X point of phonon dispersion is wrong?

lucking-pine songsong19840614 at gmail.com
Mon May 16 14:53:52 CEST 2011

Hi,
I also want to learn PlotPhon.This is a new tool since version4.2.I hope it
can solve this problem.

Bests.
Pine.

2011/5/16 Eyvaz Isaev <eyvaz_isaev at yahoo.com>

>  Hi,
>
> The way you used to generate q-points is  somewhat unusual, but seems to be
> correct.
>
> Try also PlotPhon utility in your QE suite.
>
> Bests,
> Eyvaz.
>
>  ------------------------------
> *From:* lucking-pine <songsong19840614 at gmail.com>
> *To:* PWSCF Forum <pw_forum at pwscf.org>
> *Sent:* Sat, May 14, 2011 5:04:44 AM
>
> *Subject:* Re: [Pw_forum] why K-X point of phonon dispersion is wrong?
>
> Dear Eyvaz Isaev:
> And I want to ask that  I use these k-points into <band.input>,and then the
> <band.output>will auto-transform the k-point into  Cartesian and units of
> 2*\pi/a,and I use these output k-point in <matdyn.input>.I always get
> k-point in this way.Is there something wrong?
>
> Bests,
> Pine.
>
> 2011/5/14 Eyvaz Isaev <eyvaz_isaev at yahoo.com>
>
>>  Hi,
>>
>> XCryDen gives you  q-points coordinates with respect to basis vectors.
>> But X(1,1,0) and K(3/4,3/4,0) are in Cartesian and in units of 2*\pi/a.
>>
>> If I am not wrong, matdyn.x uses (at least, always I used)  q-points in
>> Cartesian, so, you have to transform these points to Cartesian.
>> Or see a text book  (H.Jones The Theory of Brillouin zones and electronic
>> states in crystals, or J. Callaway Energy band Theory, or
>> whatever you like)   to find them in Cartesian.
>>
>>
>> Bests,
>> Eyvaz.
>>
>>  ------------------------------
>> *From:* lucking-pine <songsong19840614 at gmail.com>
>> *To:* PWSCF Forum <pw_forum at pwscf.org>
>> *Sent:* Wed, May 11, 2011 5:34:10 AM
>> *Subject:* Re: [Pw_forum] why K-X point of phonon dispersion is wrong?
>>
>> Dear Eyvaz Isaev:
>> Thank you for your advice.My k-point is chosen by Xcrysden.such as:
>> G   0.0000000000     0.0000000000     0.0000000000
>> K  -0.7500000000    -0.3750000000    -0.3750000000
>> X  -0.5000000000     0.0000000000    -0.5000000000
>> G  0.0000000000     0.0000000000     0.0000000000
>> L - 0.5000000000    -0.5000000000    -0.5000000000
>> X   0.0000000000    -0.5000000000    -0.5000000000
>> W -0.2500000000    -0.5000000000    -0.7500000000
>> L  -0.5000000000    -0.5000000000    -0.5000000000
>>
>> and I try to use your advice through using 3 type of attempt.
>> 1.only chang K,Xpoint of K-G path to K(0.75,0.75,0), X point (1, 1, 0)
>> 2.all k point multipy 2 times.
>>    such as:
>>
>> G   0.0000000000     0.0000000000     0.0000000000
>> K  -1.5000000000    -0.7500000000    -0.7500000000
>> X  -1.0000000000     0.0000000000    -1.0000000000
>> G  0.0000000000     0.0000000000     0.0000000000
>> L - 1.0000000000    -1.0000000000    -1.0000000000
>> X   0.0000000000    -1.0000000000    -1.0000000000
>> W -0.5000000000    -1.0000000000    -1.5000000000
>> L  -1.0000000000    -1.0000000000    -1.0000000000
>>
>> 3.only K,Xpoint of K-G path multiply 2 times.
>>    such as
>>
>> G   0.0000000000     0.0000000000     0.0000000000
>> K  -1.5000000000    -0.7500000000    -0.7500000000
>> X  -1.0000000000     0.0000000000    -1.0000000000
>> G  0.0000000000     0.0000000000     0.0000000000
>> L - 0.5000000000    -0.5000000000    -0.5000000000
>> X   0.0000000000    -0.5000000000    -0.5000000000
>> W -0.2500000000    -0.5000000000    -0.7500000000
>> L  -0.5000000000    -0.5000000000    -0.5000000000
>>
>> However,all this attempts yield wrong picture. So,this must be something I
>> didn't understand correctly.Would you tell me where is my fault ?
>> 2011/5/6 Eyvaz Isaev <eyvaz_isaev at yahoo.com>
>>
>>>  Hi,
>>>
>>> First of all I would recommend  the use of PlotPhon utility to plot
>>> phonon dispersion relations. For this one you have to have calculated
>>> interatomic force constants matrix (*.fc) file.
>>>
>>> Regarding your particular question: you should choose K(0.75,0.75,0),
>>> then from the  K point go to the X point (1, 1, 0) which is equivalent to
>>> the X(1,0,0) point. Then from the X(1,0,0) to the Gamma (0,0,0) point.
>>> Dashed line just means that we can continue in this direction to match
>>> phonons at the X point (i.e. it is an intermediate point from the Gamma to
>>> the X point) .
>>>
>>>
>>> Bests,
>>> Eyvaz
>>>
>>> -------------------------------------------------------------------
>>> Prof. Eyvaz Isaev,
>>> Department of Physics, Chemistry, and Biology (IFM), Linkoping
>>> University, Sweden
>>> Theoretical Physics Department, Moscow State Institute of Steel & Alloys,
>>> Russia,
>>> isaev at ifm.liu.se, eyvaz_isaev at yahoo.com
>>>
>>>
>>>  ------------------------------
>>> *From:* lucking-pine <songsong19840614 at gmail.com>
>>> *To:* Pw_forum at pwscf.org
>>> *Sent:* Fri, May 6, 2011 2:50:16 PM
>>> *Subject:* [Pw_forum] why K-X point of phonon dispersion is wrong?
>>>
>>> My pwscf is used in calculating Si phonon dispersion.The trend of picture
>>> in
>>>
>>> most special Symmetry is right.But the only K-X is wrong.I use Xcrysden
>>> to
>>>
>>> get K-point.
>>> I found most paper is dash line in 'K' point.So what is mean? Please
>>> anyone
>>>
>>> could tell me!  Thanks!
>>> The attachment is my picture and reference paper.
>>>
>>> _______________________________________________
>>> Pw_forum mailing list
>>> Pw_forum at pwscf.org
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>>>
>>>
>>
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