[Pw_forum] Selection of K point for band structure calculation

[Saif Ullah]

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>
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>
> 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 <+91%2075075%2046773>*
>>
>>
>> _______________________________________________
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>>
>>
>> --
>> Lorenzo Paulatto - Paris
>>
>>
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>
>
>
> --
>
> *Madhurya Chandel*
>
> *Research Scholar *
>
> *Department of Chemistry *
>
> *BITS PILANI, GOA campus*
>
> *+91-7507546773 <+91%2075075%2046773>*
>
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