[QE-users] Query regarding k path selection, mismatching of band gap

Vahid Askarpour vh261281 at dal.ca
Tue Oct 13 23:14:01 CEST 2020


I think for insulators, occupation =fixed in the scf calculation. The degauss value is mainly for metals. You are using a broadening of 0.02Ry=0.272eV for a gap which is only 0.04eV. This broadening will likely result in a metallic DOS, which is what you are getting. For the nscf/DOS calculation, I suggest the tetrahedron method. These are explained in the QE manual.

Cheers,
Vahid

Vahid Askarpour
Department of physics and atmospheric science
Dalhousie University
Halifax, NS

On Oct 13, 2020, at 4:49 PM, Poonam Kaushik <poonamkaushik40 at gmail.com<mailto:poonamkaushik40 at gmail.com>> wrote:

CAUTION: The Sender of this email is not from within Dalhousie.

Dear Expert,
About the first option, I used to confuse to select the correct option for the occupation, smearing type, and broadening part. In my input file, I used an 'mv' smearing with a broadening of 0.02 Ry. So either I can reduce it to 0.01 Ry or  I can try any other occupation,  like tetrahedra or fixed. my system is an insulator with a small bandgap of 0.04 eV. Also in the third option, I calculated the k path by using the CIF file, and k-pathfinder. Please correct me if I am wrong.

Thanks and regards,
Poonam Sharma




-------------------------------------------------------------------------------------------------
Poonam Sharma
Research Scholar
Department of Physics
Indian Institute of Technology Bombay
Mumbai - 400076
India.



On Wed, Oct 14, 2020 at 12:18 AM Nicola Marzari <nicola.marzari at epfl.ch<mailto:nicola.marzari at epfl.ch>> wrote:
On 13/10/2020 20:43, Poonam Kaushik wrote:
> Dear Expert,
> So the only option that I have is to include the complete path and do
> the calculation again.
> Thank you so much for your suggestion.
>

Mostly welcome, but you have three options - destiny can be generous
sometimes.

The first option would be doing a more careful DOS:
https://www.quantum-espresso.org/Doc/INPUT_DOS.html

                        nicola

>
>
> Thanks and regards,
> Poonam Sharma
>
>
>
>
> -------------------------------------------------------------------------------------------------
> Poonam Sharma
> Research Scholar
> Department of Physics
> Indian Institute of Technology Bombay
> Mumbai - 400076
> India.
>
>
>
> On Tue, Oct 13, 2020 at 11:53 PM Nicola Marzari <nicola.marzari at epfl.ch<mailto:nicola.marzari at epfl.ch>
> <mailto:nicola.marzari at epfl.ch<mailto:nicola.marzari at epfl.ch>>> wrote:
>
>
>
>
>       From the most to the less likely, it could be that your DOS has some
>     broadening that masks the existence of a small gap, or that the gap
>     closes across the last two segments of the path that you are
>     missing, or
>     that you are very unlucky and the band gaps closes at points that do
>     not
>     lie on a high symmetry path.
>
>                   nicola
>
>
>     On 13/10/2020 19:53, Poonam Kaushik wrote:
>      >
>      > Dear Experts,
>      >   I have one query regarding k path selection. After using Kpath
>     finder
>      > (https://www.materialscloud.org/work/tools/seekpath ), i got
>     this type
>      > of  k path
>      > G-M-K-G-A-L-H-A|L-M|H-K for my structure. In the calculation, I
>     used, up
>      > to G-M-K-G-A-L-H-A. So, is this ok to select a path up to this?
>      > Basically in the band structure, I am getting some finite gap
>     while in
>      > dos I m getting a zero bandgap, after selecting the path up to
>      > G-M-K-G-A-L-H-A. I am not able to figure out why this is happening?
>      > Should it help to include the complete path? I am attaching here my
>      > input file, band structure, and dos. Please have a look.
>      >
>      >
>     https://drive.google.com/drive/folders/1UhUgod8KnvdovJfxMqbJMQwdtb3dE-yY
>      >
>      >   I'll be very thankful for any suggestions.
>      >
>      > Thanks and regards,
>      > Poonam Sharma
>      >
>      >
>      >
>      >
>     -------------------------------------------------------------------------------------------------
>      > Poonam Sharma
>      > Research Scholar
>      > Department of Physics
>      > Indian Institute of Technology Bombay
>      > Mumbai - 400076
>      > India.
>      >
>      >
>      > _______________________________________________
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>
>     --
>     ----------------------------------------------------------------------
>     Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
>     Director, National Centre for Competence in Research NCCR MARVEL, EPFL
>     http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project
>


--
----------------------------------------------------------------------
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
Director, National Centre for Competence in Research NCCR MARVEL, EPFL
http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project
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