Odp: [Wien] Band Gap problem

[K. Ruebenbauer]

----- Original Message -----
From: Javad Hashemifar <s_javad at yahoo.com>
To: <wien at zeus.theochem.tuwien.ac.at>
Sent: Sunday, August 01, 2004 12:17 PM
Subject: Re: [Wien] Band Gap problem


> > I have calculated band structure of GaN in wz phase under GGA(96)
> > approximation with band gap Eg=2.2eV,while the pseudopotential and
> > Experimental data show that it is equals to 3.5eV.Who can help me in
> > some simple terms that what is the reason of this main difference
> > between these calculations.Of course,I have calculated band structure of
> > GaN with other approximations( LSDA,GGA(91) ),that is not affect.
>
> Dear Behrooz Rezaei,
> I am not expert in this field, but it seems that usual LDA based
> Exchange-correlation approximations are not appropriate for calculation of
the
> band gap of semiconductors. Peoples are developing some other
approximations
> like (Exact-Exchange method for better treatment of the band gap of
> semiconductors).
> In wien2k code, as far as I know, there is an option for exchange
correlation
> potential called Engel-Vosko approximation (PRB47, 13164) that seems to
leads
> to better band gaps rather than other approximations (LDA and GGA). In
order to
> use this approximations you have to use one of the switches 15, 25 or 26
as
> VXC-SWITCH in case.in0 input file. I think switch 25 is better but I am
not
> sure. It would be nice if some of expert wien users help more about using
this
> exchange-correlation approximation.
> Best regards,
> Javad Hashemifar
>
>
>
> =====
> --------------------------------------------------------------------------
-----
> Javad Hashemifar                                      phone : ++49-30-8413
4804
> Permanent : Physics Department, Isfahan University of Technology, Isfahan,
Iran
> Current : Fritz-Haber-Institut der MPG, Faradayweg 4-6, D-14195 Berlin,
Germany
> e-mails:  hashemi at fhi-berlin.mpg.de          &
hashemifar at ph.iut.ac.ir
> --------------------------------------------------------------------------
-----
>
>
>
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