[Pw_forum] GGA underestimates lattice constant in BaO

[Munima Bora Sahariah]

Dear Paolo

Thanks for your reply.

In fact I tried GGA(PBE) also. In this case the lattice parameter is
better than GGA(pw91) (PBE = 10.313 a.u.) but is still less than that of
LDA.

If I generate new pseudopotentials for Ba, primarily which parameters
would you suggest me to tune in order to improve the quality?

regards

munima



>
> 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
>
>
>
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Dr. Munima B. Sahariah
PI, DST Fast Track Project
IASST, Guwahati
Assam, INDIA


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