[DFTB-Plus-User] Band Gap calculation

[Sarah Gamal]

I don't think using extra K points can not be the reason,
Which type of Slater Koster files should I use?
If I used the wrong files, may this cause this large difference in the band
gap?
I used the files for solids and surfaces.

On Wed, Nov 7, 2018 at 7:16 PM Ben Hourahine <
benjamin.hourahine at strath.ac.uk> wrote:

> 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>
> 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>
>> 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
>>>
>>> [image: image1.tiff]
>>>
>>> On Nov 4, 2018, at 3:29 PM, Ben Hourahine <
>>> 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>
>>> 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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>>>
>>>
>>> --
>>>       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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> _______________________________________________
> DFTB-Plus-User mailing listDFTB-Plus-User at mailman.zfn.uni-bremen.dehttps://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
>
> 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
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