[DFTB-Plus-User] DFTB-Plus-User Digest, Vol 117, Issue 3

Thomas Niehaus thomas.niehaus at univ-lyon1.fr
Wed May 15 12:25:44 CEST 2024 

Dear Achyu,

in order to get the band gap you have to find the orbital/band that is 
the lowest in energy _and_ unoccupied and the orbital/band that is the 
highest in energy _and_ occupied. Subtract the energy of those orbitals.

Best Thomas


On 5/7/24 18:12, Achyut Subedi wrote:
> Dear Professor Niehaus,
>
> Thank you for your response.  Among the k points and 
> corresponding orbital energy values, how do we know which value 
> corresponds to the band gap?
> I couldn't attach my band.out file here to get more insight on it 
> because of size limitation.
> Which value should we pick to get the band gap?
> I have seen many authors reporting the band gap using DFTB+ 
> calculation but I am not sure how they calculate.
>
> I would be happy to be more clear on this topic. Thank you!
>
> On Tue, May 7, 2024 at 6:00 AM 
> <dftb-plus-user-request at mailman.zfn.uni-bremen.de> wrote:
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>        1. Re: Band_gap calculation in DFTB+ (Thomas Niehaus)
>
>
>     ----------------------------------------------------------------------
>
>
>     Message: 1
>     Date: Mon, 6 May 2024 16:34:14 +0200
>     From: Thomas Niehaus <thomas.niehaus at univ-lyon1.fr>
>     To: <dftb-plus-user at mailman.zfn.uni-bremen.de>
>     Subject: Re: [DFTB-Plus-User] Band_gap calculation in DFTB+
>     Message-ID: <3be399f8-5753-4337-9421-bfc8ebc47d7d at univ-lyon1.fr>
>     Content-Type: text/plain; charset="utf-8"; Format="flowed"
>
>     Hi,
>
>     the file band.out contains the information you are looking for. It
>     lists
>     for each k-Point the orbital energy and the occupation of that
>     orbital/band. Be aware that for indirect band gaps the conduction
>     band
>     minimum and the valence band maximum might be at different k-Points.
>
>     Hope that helps.
>
>     Best Thomas
>
>     On 5/3/24 18:00, Achyut Subedi wrote:
>     >
>     > I am a new DFTB+ user and I am trying to calculate the band
>     structure
>     > and Density of states for a larger system.
>     >
>     > I have got one confusion while calculating the band gap of a band
>     > structure. What I did for now is plotted the "band_tot.dat" output
>     > file in MATLAB and calculated the difference between maximum
>     valence
>     > band and lowest conduction band. But, I wanted to know if we can
>     get
>     > the band gap directly from our calculation in DFTB+ as we get in
>     DFT
>     > calculation as "Highest Occupied Molecular Orbital" and "Lowest
>     > Unoccupied Molecular Orbital" and find difference in between them.
>     >
>     >
>     > I want to know if the band gap can be directly calculated by
>     > manipulating the input files or there is another method for its
>     > calculation.
>     >
>     > I can see a lot of papers reporting the band gap calculated for a
>     > larger ( systems) but I am not sure how it was calculated.
>     >
>     >
>     > --
>     > Best Regards
>     > Er. Achyut Subedi
>     > Registered Mechanical Engineer
>     > (IOE, TU, Nepal)
>     > +977-9847703110
>     >
>     > _______________________________________________
>     > DFTB-Plus-User mailing list
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>
>
>     -- 
>     Prof. Dr. Thomas Niehaus
>     Institut Lumière Matière
>     UMR5306 CNRS
>     Université Claude Bernard Lyon 1
>     Domaine Scientifique de La Doua
>     10 rue Ada Byron
>     69622 Villeurbanne CEDEX, France
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>     End of DFTB-Plus-User Digest, Vol 117, Issue 3
>     **********************************************
>
>
>
> -- 
> Best Regards
> Er. Achyut Subedi
> Registered Mechanical Engineer
> (IOE, TU, Nepal)
> +977-9847703110
>
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-- 
Prof. Dr. Thomas Niehaus
Institut Lumière Matière
UMR5306 CNRS
Université Claude Bernard Lyon 1
Domaine Scientifique de La Doua
10 rue Ada Byron
69622 Villeurbanne CEDEX, France
--
Office: Brillouin building, 4th floor, room 006
Tel: +33 472 431 571
Home page:http://ilm-perso.univ-lyon1.fr/~tniehaus
Lab:http://ilm.univ-lyon1.fr
  

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