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

[Eyvaz Isaev]

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:
Hi,Thanks for your help.I will read these books you Recommended.
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) 
>>.
>>
>>Please also provide your affiliation.
>>
>>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.
>>_______________________________________________
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>>
>
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