[Pw_forum] alkali metal pseudopotentials

[Paolo Giannozzi]

On Saturday 31 December 2005 06:11, W. YU wrote:

> 2. I did some calculations on alkali hydrides such as
> LiH and NaH. For LiH, the LDA using Von Barth and Car
> scheme give a much smaller lattice constant

I am not sure what PP was used in this paper: G. Roma et al, 
Solid State Commun. 98, p.203 (1996), but it might well be 
the same that one finds on www.pwscf.org. They get -5.1%
for the lattice constant, -2.5% taking into account  finite
temperature and zero-point effects. Is this what you get?
it is nothing to write home about, but it is a decent result.
GGA should yield a larger lattice parameter.

> For NaH system, the VBC LDA gives a lattice constant very
> close to the experimental one and the GGA gives larger lattice
> constant.

nothing surprising here

> When the vibrating effect [...] is taken into account, the resulting
> lattice constant is much larger than the experiment. 

I don't expect finite-temperature and zero-point effects to be larger
in NaH than in LiH, so with LDA you will get something in the order
of +2% for the lattice constant. It is not very good but it isn't very
bad either

Paolo
-- 
Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
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