[DFTB-Plus-User] Band Gap calculation

[Sarah Gamal]

Any help please?

On Mon, Nov 12, 2018 at 4:02 PM Sarah Gamal <s.abouelhasab at gmail.com> wrote:

> 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
>> DFTB-Plus-User at mailman.zfn.uni-bremen.de
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>
>
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