[Pw_forum] How to simulate cation H+ without electron or Li+ with only two electrons

[Axel Kohlmeyer]

On Tue, 15 Jul 2008, vega lew wrote:

VL> 
VL> Dear all,
VL> 

VL> I want to simulate H+ without electron and Li+ with only two 
VL> electrons. How could I do this?

VL> The system I want to simulate is composed of ~100 nomoral atoms and 
VL> ~1-3 cations. The nomoral atoms has ordinary electrons such as C 
VL> with 6 electrons and Si with 14 electrons.  Cations lose some 
VL> electrons such as H+ without any electrons and Li with only 2 
VL> electrons.

please pick up your elmentary quantum chemistry text book,
read it again and realize that your question doesn't make
much sense. what do you compute in quantum chemistry?

the electronic structure in the field of the atom cores.
one fundamental outcome of quantum mechanics is that you 
cannot distinguish electrons. they have no labels and they 
don't belong to an atom or ion (even people try _very_ hard
to put them back on in postprocessing). so all you have to 
do is to determine the total number of electrons and the 
electrostatic field of the atoms (which is approximated by 
pseudopotentials, i.e. you have to sum up the valence 
electrons) and let the physics of the problem work its magic.

VL> Do you think pseudopotential with plane wave basis sets DFT 
VL> calculation is suitable for this mater?

VL> If so, which parameter I should control in Q-E to separate the 
VL> cation H+/Li+ from the atom

none. if you want to force ions to be like this, you are doing
classical mechanics. QE does not do that. depending on how
much your substrate attracts or provides electrons, you may
need to use a semi-core li potential (i.e. one with 3 valence
electrons).

cheers,
    axel.


VL> 
VL> H with 1 electron/ Li with 3 electrons? 
VL> 
VL> best wishes,
VL> 
VL> vega
VL> 
VL> Vega Lew
VL> PH.D Candidate in Chemical Engineering
VL> State Key Laboratory of Materials-oriented Chemical Engineering
VL> College of Chemistry and Chemical Engineering
VL> Nanjing University of Technology, 210009, Nanjing, Jiangsu, China
VL> _________________________________________________________________
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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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Q: what are quantum mechanics?  A: people who repair quantums, i guess.