[DFTB-Plus-User] plotting DOS and BAND with fermi energy

[Gabriele Penazzi]

On 03/25/2014 07:59 AM, ??? wrote:
> Dear DFTB user,
> I have tried to follow the DOS and Band calculation example for  TiO2
> on the dftb+ website,
> I  used exactly the same input file but different coordinate for the
> supercell,  use "dp_dos" (from dp_tool) to convert
>  the format and to plot band structure and DOS structure. By the way,
> the calculation was convergenced well.
> In this way, I found the trend of DOS  curve is similar as shown on
> website, however, the trend of Band curve
> is very different from the picture shown on website, the VBM (valence
> band maximum)  amd CBM (conductor band minmum) 
> of my result are all below of zero,and the fermi level is very close
> to the VBM, while 
> in the website stucture, VBM and CBM are distributed on both sides of
> zero point.
>  I am wondering,

Hi

> 1. does anyone know how to fix this problem?

this is not a problem. The energy reference is arbitrary therefore you
can rigidly shift the bands where you like most.

> 2. In the DOS and Band sturctures,I need to mark the fermi energy,
> so where are fermi levels in DOS and Band pictures,
> are they at the coordinate zero point or  elsewhere, which have to be
> marked manually?

The Fermi energy is in the output detail.out, you can use that as a
reference for the DOS. Note that, from a numerical point of view, in a
semiconductor at zero temperature the position of the Fermi level
doesn't really matter as long as it's in the bandgap. I.e. if the Fermi
level is close to the valence band, close to the conduction band or in
the middle, the number of occupied states is still the same.

> 3. Did "dp_dos"  and "dp_bands" can automiclly tune fermi level to
> coordinate zero point?

It wouldn't help for a semiconductor, for the reason above.

> Thank you in advance for your comments!
>
>
>
>
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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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