[DFTB-Plus-User] Band Gap calculation

[Sarah Gamal]

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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