[Pw_forum] GGA underestimates lattice constant in BaO

[Paolo Giannozzi]

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  
cases
in which the results are more sensitive than desired to the quality of
pseudopotentials  (in particular of Ba).

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