[DFTB-Plus-User] Band structure for H chain

Gabriele Penazzi gabriele.penazzi at bccms.uni-bremen.de
Thu Aug 30 18:30:21 CEST 2012


On 08/30/2012 05:53 PM, R.Perez Garcia wrote:
> Dear DFTB specialists,
>
> I been struggling with the plot of the band structure for my system.
> Unfortunately they look very unattractive...(if it is possible to say
> so:).
>
> SO I decide to make a test whit a hydrogen chain. After drawing an H
> atom at 1Angstrom, generate the cell to assure periodicity in one
> dimension and letting enough space in the other two (to avoid
> interactions as I do for my system).
> I get a nice plot where the lower energy is a bit higher that the
> value I found  in literature (~-18eV) but the behaviour is as
> expected. However the problems arise if in my unit cell I include two
> or more atoms then I start to see more and more lines (as many as
> atoms in the unit cell) and the energies are all mess-up.
>
> Is it a normal behaviour? I would like to include the pictures but I
> believe I need to send them to the one interested in seeing them.

Dear R,

I suspect that you're looking at a folded band structure and this is
confusing you.

If you double the size of the unit cell (two atoms), remember that the
first Brillouin zone is now the half and therefore all the bands are
folded inside this smaller Brillouin zone. That's why with two atoms you
will see two times the lines you see with one atom. From this point of
view, it's perfectly normal to see more lines and the two pictures
should be consistent. Do you understand what I mean?
Still, the energies shouldn't be messed up, i.e. the DOS should be the
same except for a scaling factor, you can check them and verify.

Gabriele


>
> Then, if I come back to my system in which I try to simulate a
> copolymer (whit 2 units, 2 times) and two fullerenes, may it means I
> need to make my unit cell smaller or something like that?
>
> Thank you so much in advance.
>
> Best regards: R
>
>
>
>
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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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