[Pw_forum] about GGA implementation

[Nicola Marzari]

Dear Ezad,

the gap is a property that DFT is not meant to describe
or predict. There is a long literature on the topic. You can
even have a real insulator described correctly (in exact DFT)
by a Kohn-Sham metal.

Notwithstanding this, hybrid functionals often seem to predict
Kohn-Sham gaps in closer agreement with experiments. As far as I know,
there aren't hybrid functionals implemented in pwscf yet.

Gaussian03 has an extensive choice (e.g. the HSE hybrid),
and I believe that now CPMD also has several of them.

Best luck,

			nicola

Ezad Shojaee wrote:

> 
> Hi
> i want to implement GGA approximation in my performance for TiO2 & i 
> have used GGA pseudopotentials .
> i want to know what  can i do more?  ( in order to have a better band gap )
> thanx
> 
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Prof Nicola Marzari   Department of Materials Science and Engineering
13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu