[CPMD-list] About the pseudo potential

[Axel Kohlmeyer]

On Wed, 27 Feb 2008, mano mano wrote:

MM> Dear users,

dear ???,

MM>   thanks one again for your help. I find in the library different 
MM>   kind of pseudo-potentials. I would like to know, how to choose the 
MM>   appropriate one?. another question: the paremeters of each 

hard to tell. ideally, pseudopotentials should be transferable,
i.e. give the same behavior when used in different environments
or oxidation states. for metals, especially transition or 
alkaline metals, there are frequently two choices: a minimal 
pseudopotential, that has only a small number of valence electrons,
which only works well for the plain metal or alloys, and a so-called
semi-core pseudopotential, where additional, outer core electrons
are taken into the valence shell. this is frequently required in
oxides. you can look at the ZV (valence charge) value in the 
pseudopotential report section to see which is the case. 

MM>   pseudo-potentiel are done for isolated atoms, but within a bulky 
MM>   system in which the environement influces, there is a way to take 
MM>   in consideration of this package, and how to modify the pseudo 
MM>   potentiel? thank you and good luck.

as stated before, pseudopotentials should be transferable, so the 
polarization of the remaining valence electrons should be similar to 
that of an all-electron calculation. please check out the chapter on 
pseudopotential generation in your favorate textbook or the 
pseudopotential tutorial of the fhi98pp package. those explanations are 
better than anything i can come up here. it is in general highly 
recommended to put some effort into understanding the pseudopotential 
generation process. this helps enormously to get a better understanding 
of the whole plane-wave-pseudopotential method.

cheers,
    axel.


MM> 
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-- 
=======================================================================
Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
   Center for Molecular Modeling   --   University of Pennsylvania
Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
tel: 1-215-898-1582,  fax: 1-215-573-6233,  office-tel: 1-215-898-5425
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