[DFTB-Plus-User] DOS of Fluorographene

Bálint Aradi balint.aradi at bccms.uni-bremen.de
Mon Apr 21 11:56:04 CEST 2014


Dear Piali Aditya,

> I am using an optimized super-cell geometry(C48F48- lattice parameters:
> a=2.58*4, b=3*4.47, C-C=1.56A and C-F =1.39A) to calculate the density
> of states of fluorographene. The slater-koster files I am using are
> consistent with the pbe functional. However, I don't get the correct
> band gap. The GGA band gap is around 3.5ev, however I keep getting 7eV.
> I have attached the input file and the DOS plot. Any insight on why this
> might be happening? Please not that I plotted E-EF(eV) on the x axis.

Depending on the parametrization, DFTB calculations may give larger gaps 
than GGA does. Note, that you use a minimal basis and several 
approximations to get ca. two orders of magnitude speedup compared to 
normal GGA calculations, so you can't expect it to reproduce GGA results 
exactly. Actually, some of the parameters were created to yield a 
correct gap (experimental though, not the incorrect GGA one), but not 
all of them.

   Best regards,

     Bálint

-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.bccms.uni-bremen.de/cms/people/b_aradi/



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