[Wien] TPSS or others?

[Peter Blaha]

TPSS (a "meta-GGA") is implemented only with E-XC, but uses the PBE V-XC.
Thus the bandstructure (gap) will not change. In addition it was already 
shown by others that even the TPSS potential will not improve this.

(maybe even the "exact" DFT functional will not improve this, because DFT
is a groundstate theory, while the gap is an excited state property and
the known "discontinuity-problem" should contribute to the gap in any
case.)  Thus one might need an "excited state" calculation (like GW,..)
in any case.

Nevertheless, a "pragmatic" and simple way on improving the gap within
WIEN2k is using the   EV-GGA (option 25 in case.in0). It should give
significantly better gaps in semiconductors (not quite the accuracy of GW,
but not too bad either in many cases). However, NEVER use this EV-GGA for
total energies (structural optimization), since this give VERY bad results.

Regards 


>   Recently I focus on the semiconductor, I know LDA and GGA(91,96) is not
> good
> 
> Enough for bandstruct of semiconductor, I tried and was nearly 50% lower for
> bandgap. Have 
> 
> Someone tried the TPSS, was that ok for semiconductor, and how was the
> result comparing 
> 
> With GW in pseudopotential? Would you please give me some advices or
> information or tips
> 
> On using TPSS?
> 
>  
> 
> Thank you very much 
> 
>  
> 
> hao
> 
>  
> 
> 


                                      P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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