[DFTB-Plus-User] Band gap of graphene

[Gabriele Penazzi]

On 07/09/2014 07:51 AM, SRKC Sharma Yamijala wrote:
> Dear all,
>
> Band gap problme is solved (I have been interpreting the results in a
> wrong manner for the last few days [I was plotting with wrong
> Fermi-energy value]. Kindly, excuse me in this regard.), but I need to
> know whether the SCC convergence is going correctly or not. Every
> "Geometry step" is getting completed by running only one SCC
> iteration. In manual example it is not so. Kindly, help me.

Dear Sharma,

it is perfectly fine, it depends on the system. The SCC correction kicks
in when there is some charge displacement between atoms. As your system
is homogeneous and all the carbon have the same coordination, you can
expect the SCC correction to be nearly zero.

Best,
Gabriele


>
> The last few lines of the output of my system are as below:
>
>
> ********************************************************************************
> ** Geometry step: 25, Lattice step: 10
> ********************************************************************************
>
>   iSCC Total electronic   Diff electronic      SCC error
>     1   -0.55899164E+02    0.00000000E+00    0.20237145E-11
>
>  Total Energy:                     -54.9846405060 H
>  Total Mermin free energy:         -54.9846405060 H
>  Volume:                             0.171654E+05 au^3
>  Pressure:                           0.854991E-09 au     0.251547E+05 Pa
>  Maximal force component:            0.600174E-05
>  Maximal Lattice force component:    0.244084E-04 au
> >> Charges saved for restart in charges.bin
>
> ********************************************************************************
> ** Geometry step: 26, Lattice step: 10
> ********************************************************************************
>
>   iSCC Total electronic   Diff electronic      SCC error
>     1   -0.55899164E+02    0.00000000E+00    0.20237145E-11
>
>  Total Energy:                     -54.9846405060 H
>  Total Mermin free energy:         -54.9846405060 H
>  Volume:                             0.171654E+05 au^3
>  Pressure:                           0.854991E-09 au     0.251547E+05 Pa
>  Maximal force component:            0.600174E-05
>  Maximal Lattice force component:    0.244084E-04 au
> >> Charges saved for restart in charges.bin
>
>  Geometry converged
>
>
> Sincerely,
> Sharma.
>
>
>
>
>
>
>
>
> ********************************************************
> *Chaitanya Sharma,*
> *Prof. Pati'*s group,
> Chemistry and Physics Materials unit,
> JNCASR, BANGLORE,
> Lab:: (080-2208) 2581, 2809
> https://sites.google.com/site/sharmasrkcyamijala/
> *********************************************************
>
>
> On Tue, Jul 8, 2014 at 7:56 PM, SRKC Sharma Yamijala
> <sharmajncasr at gmail.com <mailto:sharmajncasr at gmail.com>> wrote:
>
>     Dear DFTB+ community members,
>
>     Following the DFTB+ manual and recipes, I set up the optimization
>     calculation for graphene. When I have plotted the DOS, instead of
>     attaining a zero-band-gap semiconductor, I found an insulator with
>     ~3 eV gap. I have tried with both mio and 3ob SKF files. I have
>     attached the input and DOS for the reference. 
>
>     It would be a great help for me if any one of you can point out
>     the mistake.
>
>     I have seen many papers using DFTB+ to study Graphene/G-NRs/G-QDs.
>     So, I hope at least somebody can provide their input file and the
>     corresponding SKF files to help me to start a new project.
>
>     Thanking you for your support,
>     Sincerely,
>     Chaitanya Sharma.
>
>     P. S.: I have already seen all the threads starting from 2007 to
>     2014 (and I have been following the forum from the last 2 months)
>     and I couldn't find a problem of this kind (except one and which
>     is unanswered). From recent threads I found that,*Dr. Anusha and
>     Dr. /Bálint Aradi/* are discussing on GNRs, so I request them to
>     help me in this regard, if they can.
>
>
>
>
>
>
>
>     ********************************************************
>     *Chaitanya Sharma,*
>     *Prof. Pati'*s group,
>     Chemistry and Physics Materials unit,
>     JNCASR, BANGLORE,
>     Lab:: (080-2208) 2581, 2809
>     https://sites.google.com/site/sharmasrkcyamijala/
>     *********************************************************
>
>
>
>
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-- 
Dr. Gabriele Penazzi
BCCMS - University of Bremen

http://www.bccms.uni-bremen.de/
http://sites.google.com/site/gabrielepenazzi/

phone: +49 (0) 421 218 62337
fax: +49 (0) 421 218 62770

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