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

[lucking-pine]

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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