[Pw_forum] GGA underestimates lattice constant in BaO

Paolo Giannozzi giannozz at democritos.it
Fri Aug 1 09:06:27 CEST 2008

On Jul 23, 2008, at 7:58 , Munima Bora Sahariah wrote:

> For last couple of days I have been trying to find the equilibrium  
> lattice
> constant of BaO with GGA (pw91) and has found that  my calculated  
> value
> underestimates the experimental one by 1.3% (GGA = 10.301 a.u., EXP =
> 10.431 a.u.). Surprizingly, while trying with LDA, I obtained a value
> which is closer to the experimental one as compared to GGA (LDA =  
> 10.324
> a.u.) [...]
> While doing a search on the web, I found one paper (Phys. Rev. B 71,
> 085203) where GGA and LDA results for lattice constant of BaO have  
> been
> listed. In this paper calculations were done in CASTEP. Here the  
> LDA value
> underestimates the experimental lattice constant while the GGA 
> (pw91) value
> improves the situation and is closer to the experimental one.

try different pseudopotentials if you can: this might be one of those  
in which the results are more sensitive than desired to the quality of
pseudopotentials  (in particular of Ba).

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

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