[Wien] band gap problem

[Krzysztof Osuch]

Just a short comment:

DFT has been extended to excited states by L. Fritsche - see for
example : L. Fritsche, Physica B 172, 7-17 (1991) and references
therein.

Regards

K. Osuch





On Wed, 2004-04-07 at 15:37, Jorissen Kevin wrote:
> As you may know, DFT is a ground state theory and in fact there's no theoretical justification for using excited states from a DFT calculation.  Therefore, spectra may be completely wrong - not only the band gap, but also the fine structure, ...
> However, in quite a lot of cases, we see that DFT reproduces spectra quite well.  To summarize, 'we use it because it often works out'.
> Band gaps, however, are often wrong (that doesn't mean trends - such as the change of a band gap due to impurities, strain, ... - are necessarily wrong, too); another famous example is the branching ratio, which can only be reproduced by more sophisticated methods (eg TDLDA).
>  
> 
> Kevin.
>  
> 
> 	-----Oorspronkelijk bericht----- 
> 	Van: M.Y.Wu [mailto:M.Y.Wu at tnw.tudelft.nl] 
> 	Verzonden: wo 4/7/2004 1:23 
> 	Aan: wien-zeus.theochem.tuwien.ac.at 
> 	CC: 
> 	Onderwerp: [Wien] band gap problem
> 	
> 	
> 
> 	Dear Wienuser,
> 	
> 	I got a question related to the band gap. From the ML, I know there is an
> 	underestimation for the band gap. Does it affect xspec, elnes optic
> 	simulation? If the material is an insulator or semiconductor from
> 	experiment, but the calculation get a conductor. Will the xspec, elnes and
> 	optic simulations from that still be reasonable or totally meaningless?
> 	
> 	
> 	
> 	Best regards,
> 	Mengyue
> 	*******************************
> 	Dr. Meng-Yue Wu
> 	Kavli institute of nanoscience Deflt
> 	Rotterdamseweg 137,
> 	2628 AL Delft, The Netherlands
> 	Tel:+31-15-2784796 (office)
> 	Fax:+31-15-2786730
> 	Email address: M.Y.Wu at tnw.tudelft.nl
> 	
> 	
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