[Pw_forum] van der waals force

[Axel Kohlmeyer]

2009/5/19 Mehrnaz Anvari <anvari_meh at physics.iust.ac.ir>:
> Dear axel
> Thanks a lot because of your answer. As you said I am trying to understand
> the DFT-D method. Now I have another question about difference between
> pseudo potential code & full one. Is the latter suitable for dispersion

dear mehrnaz,

this question can be answered with common sense. there are
two points to consider:
a) pseudopotentials integrate out core electrons. can you imagine
   those to contribute to dispersion interactions?
b) if using pseudopotentials would give you (significantly) different
  results than an all electron calculation, would it make sense to use
  pseudopotentials in the first place?

> force. I mean when we use full potential for certain atom is it compatible
> with the potential of this atom in crystal?

a well built and transferable pseudopotential should be behave like the
original atom and in principle the code should not care about it, i.e. you
can mix and match pseudopotentials with different number of valence
electrons for the same element and should get the same structure (unless
the semi-core electrons have a significant contribution, e.g. in highly oxidized
environments).

the problem of insufficient dispersion interactions in DFT manifests itself
in the incorrect asymptotic distribution of the density far away from atoms.

cheers,
    axel.

> By the way I 'll become happy if someone answer my second question in
> previous mail
> Best Regards
> Mehrnaz Anvari
> Iran University Of Science & Technology
>
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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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