[Pw_forum] alkali metal pseudopotentials

[W. YU]

Dear PW users,

Happy and brighter new year!

I have some problmes on using the alkali
pseudopotentials;

1. Has anybody know any real system usage of the
pseudopotenals of Li, Na, and K (both LDA and GGA)
provided by the PW web? 

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 while GGA
using uspp and a ld1-generated TM type Norm-conserving
LDA pseudopotential or the LDA pseudopotential
converted from FHI format give much larger lattice
constants than the experimental result. Bearing in
mind the small mass of this system, the vibrating
energy should play an important role and the
theoretical LDA lattice constant would be much
smaller. For NaH system, the VBC LDA gives a lattice
constant very close to the experimental one and the
GGA gives larger lattice constant. When the vibrating
effect (Zero point energy and temperature effect) is
taken into account, the resulting lattice constant is
much larger than the experiment. While a
full-potential calculation  with both LDA and GGA give
much smaller lattice constants for both LiH and NaH
than experimental ones. Now it seems that the
calculations using pseudopotentials cannot give
systematic results for LiH and NaH even with VBC
norm-conserving pseudopotentials---that is, a much
smaller zero-temperature lattice constant with a major
improvement when the zero-point energy is included,
but still less than or just close to the experimental
one. 

(Note, the none-linear-core corrections are used on
all alkali atom pseudopotentials).

In this case, can I still trust the pseudopotential of
Li and/or Na?

thanks a lot!

W. YU

 


		
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