[Pw_forum] Selection of K point for band structure calculation

Fri Nov 10 08:32:25 CET 2017

Dear Valentina,
The CIF parser that I use in seekpath is the one provided by ASE, that however sometimes fails with some CIF files.
I am planning of including a more complete one - in the meantime, could you send me (in private) a CIF file that does not work, so I can check what the problem is?

Thanks in advance,
Giovanni Pizzi

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Giovanni Pizzi
Theory and Simulation of Materials and MARVEL, EPFL
http://people.epfl.ch/giovanni.pizzi
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On 8 Nov 2017, at 21:10, Valentina Shvets <valentinashvets58 at gmail.com<mailto:valentinashvets58 at gmail.com>> wrote:

The resource http://materialscloud.org/tools/seekpath/input_structure is excellent, however, it does not read the files with the extension, *.сif, which I take from the resource COD (www.crystallography.net<http://www.crystallography.net/>). Could you kindly inform which information and in what format should be entered in the resource you created to calculate the k-points data required for Quantum ESPRESSO pw.x input.
With kind regard,
V. Shvets

On Mon, Oct 23, 2017 at 7:22 PM, Saif Ullah <kiterunner7 at gmail.com<mailto:kiterunner7 at gmail.com>> wrote:
How to decide that? For inverse spinel (CuFe2O4) with FCC structure (56 atoms), what is the minimum number of K point (approx) required?

There is no such thing like minimum or maximum. You need to look at your bands. If it is smooth, then the number is fine. To be on a safer side, I would recommend 50 along each of the high symmetry points. If your cell is too small, then you need to increase and vice versa.

Regards
Saif
Department of Physics, UFJF, Brazil

On Mon, Oct 23, 2017 at 2:55 PM, Madhurya Chandel <madhurya.svnit at gmail.com<mailto:madhurya.svnit at gmail.com>> wrote:
Thank you for your kind reply.

The number of points is free, but you have to take it large enough that the bands look smooth and not jagged.

How to decide that? For inverse spinel (CuFe2O4) with FCC structure (56 atoms), what is the minimium number of K point (approx) required?

Also, the continuity analysis done by bands.x
what is the continuity analysis?

 You just need to go through the high symmetry points. The link may be useful:  http://web.mit.edu/xcrysden_v1.5.60/www/XCRYSDEN/doc/kpath.html)
Thank you for your help but I already referred this

With regards
Madhurya

On Mon, Oct 23, 2017 at 6:09 PM, Lorenzo Paulatto <paulatz at gmail.com<mailto:paulatz at gmail.com>> wrote:
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?

Hello,

I also recommend trying the seekpath online tool <http://materialscloud.org/tools/seekpath/input_structure/><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<tel:+91%2075075%2046773>

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Lorenzo Paulatto - Paris

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Madhurya Chandel
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BITS PILANI, GOA campus
+91-7507546773<tel:+91%2075075%2046773>

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