[CPMD-list] PP

[Axel Kohlmeyer]

On 7/20/06, GU ZHIHUI <zhihui.gu at chemail.tamu.edu> wrote:

since ari already covered the first part of your question,
here a comment to the second part:

> By the way, Could anyone gives me some suggestions about the R cutoff for
> valence orbitals and R core cutoff??

finding good cutoff values for the various channels in pseudopotentials
is part of the 'black magic' behind creating psp-generation. there are
a few rules that you have to follow (e.g. r_c must be large enough, that
there is no node in the corresponding all-electron wavefunction for
all r > r_c),
but then there are also several 'should be' rules (e.g. the r_c for different
channels should be very similar) that can help to avoid ghost states and
finally you have the property, that smaller r_c may increase transferability
at the cost of needing a higher plane wave energy cutoff.

for a good introduction into creating norm-conserving pseudopotentials
and the associated pitfalls, i would recommend looking at the fhi98pp
code and the associated tutorial. see:
http://www.fhi-berlin.mpg.de/th/fhi98md/fhi98PP/index.html
what is stated here applies to CPMD as (in fact you can even convert
the fhi98pp generated pseudopotentials to CPMD format). the atomc
code is lacking most of the pp-testing instrumentation, so you have
to test those potentials directly with CPMD.

regards,
    axel.

> Many thanks!!
>
>
> Zhihui Gu
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>
>
>


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Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
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