[Pw_forum] Band_structure_plot

[Giovanni Cantele]

> On 05 Jul 2015, at 18:29, Gul Rahman <gulrahman at qau.edu.pk> wrote:
> 
> Dear All,
> I am doing some test calculations on 2D Sn and comparing QE with SIESTA. Both QE and SIESTA almost give the same results (DOS, lattice constnat, charge,,). However, I have problem with the band structure. I want to plot  the band structure in 
> 0.0,0.0 0.0 to 0.33,0.330.00 to 0.5,0.0,0.0.
> I either write a python code or jut do by hand to put the number of points in the input file for the band structure calculation.
> _POINTS crystal
> 29
> 0.00000 0.00000 0.00000 1.0000
> 0.03000 0.03000 0.00000 1.0000
> 0.06000 0.06000 0.00000 1.0000
> 0.09000 0.09000 0.00000 1.0000
> 0.12000 0.12000 0.00000 1.0000
> 0.15000 0.15000 0.00000 1.0000
> 0.18000 0.18000 0.00000 1.0000
> 0.21000 0.21000 0.00000 1.0000
> 0.24000 0.24000 0.00000 1.0000
> 0.27000 0.27000 0.00000 1.0000
> 0.30000 0.30000 0.00000 1.0000
> 0.33000 0.33000 0.00000 1.0000
> 0.34000 0.31060 0.00000 1.0000
> 0.35000 0.29120 0.00000 1.0000
> 0.36000 0.27180 0.00000 1.0000
> 0.37000 0.25240 0.00000 1.0000
> 0.38000 0.23300 0.00000 1.0000
> 0.39000 0.21360 0.00000 1.0000
> 0.40000 0.19420 0.00000 1.0000
> 0.41000 0.17480 0.00000 1.0000
> 0.42000 0.15540 0.00000 1.0000
> 0.43000 0.13600 0.00000 1.0000
> 0.44000 0.11660 0.00000 1.0000
> 0.45000 0.09720 0.00000 1.0000
> 0.46000 0.07780 0.00000 1.0000
> 0.47000 0.05840 0.00000 1.0000
> 0.48000 0.03900 0.00000 1.0000
> 0.49000 0.01960 0.00000 1.0000
> 0.50000 0.00020 0.00000 1.0000
> 
> when I used it, I always see crossing points in the band structure. Pls, see the attached file and you can see crossing points not only around Dirac point, but also above that.
> Could you plz let me know why I am facing this problem whenever I try the band structure of any material and I will have these crossing lines.

Are you referring to the crossings around -1.5 and + 1.5 eV? These are just spurious, and are due to the fact that because consecutive points are connected in the plot, if the ordering of the bands is not the proper one, a point in a lower bands is connected not to the next point in the same band but to a point in a higher band. Plotting the band structure only with points or calculating the band structure with a larger number of k-points solves the problem,

Other crossings (e.g. around 4 eV) are instead the results of the calculation, so if you do not expect them it means that your input files do contain some error (e.g. k-points coordinates).
> 
> Is there any option in QE for calculating these points by just giving the high symmetry points in the input for band structure calculations.

Yes, with the latest version. You can specify a k-point path as follows:

K_POINTS { crystal_b }
5
gG    50
M     50
X     50
R     50
gG     1

which corresponds to 5-1=4 lines in the Brillouin zone of a simple cubic lattice, that s, Gamma-M, M-X, X-R, R-Gamma, each sampled with 50 points. The point labels that are recognised are shown in detail in espresso-5.2.0/Doc/brillouin_zones.pdf

Giovanni


> Thanks,
> Gul   
> 
> -- 
>  
> Dr. Gul Rahman
> Assistant Professor,
> Department of Physics,
> Quaid-i-Azam University,
> Islamabad, Pakistan
> http://www.qau.edu.pk/profile.php?id=818020 <http://www.qau.edu.pk/profile.php?id=818020><bands.ps>_______________________________________________
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-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele

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