[DFTB-Plus-User] Band Gap calculation

[Ben Hourahine]

Hello Sarah,

might the the extra points in DFTB be at locations in the Brilouin zone
where the gap is smaller and which are not sampled for siesta/espresso?

Regards

Ben

On 05/11/2018 11:28, Sarah Gamal wrote:
>
> 1)Are you comparing equivalent k-points between the different codes?
>
>
> *Yes and I used more KPOINTS in DFTB*
>
> 2) What DFT functional are you using? DFTB functional tends to be
> similar to GGA but with an overestimation of the gap in most cases
> (LDA might be giving a smaller value).
>
> *We have used GGA in DFT *
>
>
> 3) Is there anything special about the electronic structure of this
> system (flat band correlation effects in moiré graphene)?
>
>
> *Not pure flat, see attached file (black for spin up and blue for spin
> down) *
>
> Regards
>
> On Mon, Nov 5, 2018 at 1:19 PM Sarah Gamal <s.abouelhasab at gmail.com
> <mailto:s.abouelhasab at gmail.com>> wrote:
>
>     1)Are you comparing equivalent k-points between the different codes?
>
>
>     *Yes and I used more KPOINTS in DFTB*
>
>     2) What DFT functional are you using? DFTB functional tends to be
>     similar to GGA but with an overestimation of the gap in most cases
>     (LDA might be giving a smaller value).
>
>     *We have used GGA in DFT *
>
>
>     3) Is there anything special about the electronic structure of
>     this system (flat band correlation effects in moiré graphene)?
>
>
>     *Not pure flat, see attached file (black for spin up and blue for
>     spin down) *
>
>     Regards
>
>     On Mon, Nov 5, 2018 at 8:01 AM Sarah Gamal
>     <s.abouelhasab at gmail.com <mailto:s.abouelhasab at gmail.com>> wrote:
>
>         1)Are you comparing equivalent k-points between the different
>         codes? 
>
>
>         *Yes and I used more KPOINTS in DFTB*
>
>         2) What DFT functional are you using? DFTB functional tends to
>         be similar to GGA but with an overestimation of the gap in
>         most cases (LDA might be giving a smaller value).
>
>         *We have used GGA in DFT *
>
>
>         3) Is there anything special about the electronic structure of
>         this system (flat band correlation effects in moiré graphene)?
>
>
>         *Not pure flat, see attached file (black for spin up and blue
>         for spin down) *
>
>         Regards
>
>         image1.tiff
>
>         On Nov 4, 2018, at 3:29 PM, Ben Hourahine
>         <benjamin.hourahine at strath.ac.uk
>         <mailto:benjamin.hourahine at strath.ac.uk>> wrote:
>
>>         Hello Sarah,
>>
>>         Thoughts so far:
>>
>>         1) Are you comparing equivalent k-points between the
>>         different codes?
>>
>>         2) What DFT functional are you using? DFTB functional tends
>>         to be similar to GGA but with an overestimation of the gap in
>>         most cases (LDA might be giving a smaller value).
>>
>>         3) Is there anything special about the electronic structure
>>         of this system (flat band correlation effects in moiré graphene)?
>>
>>         Regards
>>
>>         Ben
>>
>>         On 04/11/18 10:58, Sarah Gamal wrote:
>>>         This is the right file.
>>>         Sorry for the disturbance.
>>>
>>>         On Sun, Nov 4, 2018 at 12:56 PM Sarah Gamal
>>>         <s.abouelhasab at gmail.com <mailto:s.abouelhasab at gmail.com>>
>>>         wrote:
>>>
>>>             Dear,
>>>             I am working on a project and we need to calculate the
>>>             band gap for graphene nanomesh.
>>>             The band gap was calculated for the same system by
>>>             siesta and espresso and it was 0.7 eV.
>>>             When it's calculated by DFTB+ it was about 0.185 eV.
>>>
>>>             What do you think the problem?
>>>             I attached the input file, should I add any parameters?
>>>
>>>
>>>
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>>>         https://mailman.zfn.uni-bremen.de/cgi-bin/mailman/listinfo/dftb-plus-user
>>
>>         -- 
>>               Dr. B. Hourahine, SUPA, Department of Physics,
>>             University of Strathclyde, John Anderson Building,
>>                     107 Rottenrow, Glasgow G4 0NG, UK.
>>             +44 141 548 2325, benjamin.hourahine at strath.ac.uk <mailto:benjamin.hourahine at strath.ac.uk>
>>
>>         2013/4 THE Awards Entrepreneurial University of the Year
>>               2012/13 THE Awards UK University of the Year
>>
>>            The University of Strathclyde is a charitable body,
>>                 registered in Scotland, number SC015263
>>         _______________________________________________
>>         DFTB-Plus-User mailing list
>>         DFTB-Plus-User at mailman.zfn.uni-bremen.de
>>         <mailto:DFTB-Plus-User at mailman.zfn.uni-bremen.de>
>>         https://mailman.zfn.uni-bremen.de/cgi-bin/mailman/listinfo/dftb-plus-user
>
>
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-- 
      Dr. B. Hourahine, SUPA, Department of Physics,
    University of Strathclyde, John Anderson Building,
            107 Rottenrow, Glasgow G4 0NG, UK.
    +44 141 548 2325, benjamin.hourahine at strath.ac.uk

2013/4 THE Awards Entrepreneurial University of the Year
      2012/13 THE Awards UK University of the Year

   The University of Strathclyde is a charitable body,
        registered in Scotland, number SC015263

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