[Pw_forum] problems with Ta2O5 compound

[Paolo Giannozzi]

On Mar 31, 2010, at 10:37 , Maxim Ivanov wrote:
> First of all energy gap is too small
>
this is a well known problem of DFT
> Moreover I have not find defect level in 14, 42, 168 atoms  
> supercells with oxygen vacancy in the center of the cell.
>
oxides are notoriously nasty stuff, in which sometimes you don't get  
things right
> Ta has 3 d electrons and is described by ultrasoft pseudopotential.  
> I took it from pwscf.org. It might be problem in the potential.
>
why should the problem be in the pseudopotential? any evidence, or  
any other
calculations to compare with?

P.
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Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222