[DFTB-Plus-User] Bandgap of GNR

[u3129004 at edu.gifu-u.ac.jp]

Dear Gabriele,

Thank you very much for your advice and teaching. 
Thank to you, using small boadening factor I could get the same result 
with yours. I would like to ask you additional questions:

*How should I decide whether structure is optimized or not? 
*And in order to optimize this geometry, how should I change the 
parameter?

Sincerely yours,
Kazuma

----- Original Message -----
> Dear Kazuma,
> 
> the distance between layers in x direction is very large and there's 
no
> interaction between periodic images along x, therefore the band would 
be
> flat. You only need sampling beyond Gamma along direction with
> interaction between periodic images, y in your case.
> 
> You structure is going to relax if allowed to, therefore the geometry 
is
> not optimized. In particular the C-H bond is shorter than the mio sk 
set
> would deliver.
> 
> I used a small broadening factor in the DOS (0.01) to clearly
> distinguish the energy levels, or alternatively you can look for the
> highest occupied and lowest unoccupied level in the detailed.out. If I
> use the default broadening I get a very similar curve to yours, there'
s
> nothing wrong with it.
> 
> You're probably trying to decide how large the gap is checking where 
the
> DOS goes to zero, but this is somewhat arbitrary because the DOS is 
also
> calculate given a finite broadening.
> 
> If you try to calculate the band structure instead of the DOS you'll 
see
> the gap more clearly.
> 
> Best,
> Gabriele
> 
> 
> On 01/13/2016 11:31 AM, u3129004 at edu.gifu-u.ac.jp wrote:
> > Dear Gabriele,
> > 
> > Thank you very much for your early reply. I have questions.
> > 
> > *Why I do not need k-points in x direction?
> > *I do not know the meaning you said "your structure seemed not 
optimized
> > ".
> > 
> > In addition, I tried again,but the result is like an attached file. 
what 
> > is the cause that my result do not agree with your result? I also 
> > attached the input file.
> > 
> > Sincerely yours,
> > Kazuma 
> > 
> > ----- Original Message -----
> >> Hi Kazuma,
> >>
> >> you don't need k-points in x direction here. I've run your input 
with
> >> the supercell folding set to 1 in x direction (left 25 in y). I 
> > lowered
> >> the force tolerance to 1e-3 too (didn't want to wait too long) and 
I 
> > get
> >> 1.42 eV (detail of dos around gap attached). Your structure seemed 
not
> >> optimized but this should not be the problem, even if I run the 
input 
> > as
> >> it is with the geometry you sent but removing optimization I get
> >> something around 1.3 eV. Maybe you do some mistake when evaluating 
the 
> > gap.
> >>
> >> Best
> >> Gabriele
> >>
> >>
> >> On 01/13/2016 10:04 AM, u3129004 at edu.gifu-u.ac.jp wrote:
> >>> Dear DFTB+ user,
> >>>
> >>> I calculated Density of states of graphene nanoribbon (please 
refer 
> > to 
> >>> an attached file). But I am doubtful of this result. Because the 
> > bandgap 
> >>> is a lot different from other calculation results which are 
> > calculated 
> >>> by Tight Binding method and first principal calculation. I 
attached 
> > my 
> >>> input file for this calculation.
> >>>
> >>> It would be very helpful if you could provide me any advice.
> >>>
> >>> Thank you in advance,
> >>> Kazuma
> >>> ---------------------------------------------------
> >>> Kazuma KIHIRA
> >>> Environmental & Renewable Energy Systems Division
> >>> Graduate School of Engineering, Gifu University
> >>> E-mail:u3129004 at edu.gifu-u.ac.jp
> >>> ---------------------------------------------------
> >>>
> >>>
> >>>
> >>> _______________________________________________
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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
> >> mobile: +49 (0) 151 19650383
> >>  
> >> _______________________________________________
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> > 
> >>
> >>
> >>
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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
> mobile: +49 (0) 151 19650383
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