[Wien] Band Gap problem

[Naeini Ashkan]

Dear Behrooz

The Problem of electronic band gap is of more fundemental nature in DFT
approach. The reasen is that in the eigenvalues of Kohn-Sham equation have
nothing to do with the eigenvalues of schroedinger, except for the highest
occopied band, e.g. fermi niveau. In order to get the right values someone
needs to add  quasi-particle correction terms  likes GWA or RPA to consider
the quasi-particle nature of vacancies.

best regards,

Ashkan Naeini



-----Original Message-----
From: Rezaei Behrooz [mailto:b.rezaei at tabrizu.ac.ir] 
Sent: Saturday, July 31, 2004 5:54 AM
To: wien at zeus.theochem.tuwien.ac.at
Subject: [Wien] Band Gap problem


Dear all wien users

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. Thank you
very much in advance. best wishes,
================================================================
Behrooz Rezaei                              Email: b.rezaei at tabrizu.ac.ir
Research Institute for Applied Physics and Astronomy 
Tabriz University                               phone: +98-411-3393008 
Tabriz, Iran                                      Fax: +98-411-3347050 
===================================================================

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