[Pw_forum] shift of energy

[Gabriele Sclauzero]

Yes, 

   I perfectly agree with Eyvaz! Moreover the experimental bandgap is underestimated within LDA or GGA, and for 4H-SiC you would get about 2.2-2.3 eV with LDA. 

   How do you measure the bandgap? Beware that in the fundamental cell the bandgap is not a direct one, but it might become such when you use a supercell (because of the refolding of the Brillouin zones).


HTH

GS

Il giorno 03/apr/2011, alle ore 10.59, Eyvaz Isaev ha scritto:

> Hi, 
>  
> >The bandgap of 8-atoms is around 10-12 eV, 
> >but that of 72-atom is around 5-7 eV.
>  
> This is unbelievable, as SiC is an indirect band gap semiconductor and 
> the bandgap is around (2.5 - 3)eV depending on crystal modification 
> (3C-SiC, 2H-SiC; 4H-SiC; 6H-SiC, etc.). 
> See http://www.matprop.ru/SiC_bandstr
> 
> So, check carefully your input/output files.
> 
> Bests,
> Eyvaz.
> 
> -------------------------------------------------------------------
> Prof. Eyvaz Isaev, 
> Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden 
> Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, 
> isaev at ifm.liu.se, eyvaz_isaev at yahoo.com
> 
> 
> From: pari shok <parishok at gmail.com>
> To: pw_forum at pwscf.org
> Sent: Sun, April 3, 2011 1:34:51 AM
> Subject: [Pw_forum] shift of energy
> 
> Dear Paolo,
> DOS of 72-atom SiC shows a shift of energy with respect to 8-atom SiC.The bandgap of 8-atoms is around 10-12 eV, but that of 72-atom is around 5-7 eV.
> Would you please help me to understand this shift.
> 
> Thanks again.
> P Shok
> UMD
> On Apr 1, 2011, at 21:36 , pari shok wrote:
> 
> > The DOS of 72-atom SiC (supercell) shows a shift of energy.
> 
> a shift with respect to what?
> ---
> Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
> 
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
> 
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§ Gabriele Sclauzero, EPFL SB ITP CSEA
   PH H2 462, Station 3, CH-1015 Lausanne

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