[Pw_forum] Selection of K point for band structure calculation

Lorenzo Paulatto paulatz at gmail.com
Mon Oct 23 14:39:06 CEST 2017

On 21/10/17 12:59, Madhurya Chandel wrote:
> Respected QE Users
> 1)I have a doubt that how to choose the number of K point for band 
> structure calculation using Xcysden K path selection?


I also recommend trying the seekpath online tool 
<http://materialscloud.org/tools/seekpath/input_structure/>, it is a bit 
easier than xcrysden to use for this task, as it also suggests a 
possible choice of path. The number of points is free, but you have to 
take it large enough that the bands look smooth and not jagged. Also the 
continuity analysis done by bands.x may not work if too few points are 
present. Note that if you use the tpiba_b or crystal_b format for the 
points, you only need to specify the path high-symmetry turning points, 
and the number of k-points in between (check the manual)

> 2) while doing the band structure calculation how to chose Fermi 
> energy (=  eV), deltaE and reference energy? Do these values affect 
> the band structure plot?

They do not, it is just a rigid shift. It is customary to shift the 
bands so that the Fermi energy is at zero. Of course, if your material 
is an insulator there is not Fermi energy, if you have empty bands you 
can take it in the middle of the gap (average of highest occupied and 
lowest unoccupied energy levels). All these values are printed at the 
end of any SCF and NSCF (not BANDS) calculation, check the output file.

hope this helps

> Thanking you
> With regards
> *Madhurya Chandel*
> *Research Scholar
> *
> *Department of Chemistry
> *
> *BITS PILANI, GOA campus
> *
> *+91-7507546773*
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> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum

Lorenzo Paulatto - Paris

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