[Pw_forum] Atomic rho

[Axel Kohlmeyer]

On Mon, 13 Oct 2008, Leonardo Matheus wrote:

LM> Hello,

hello leonardo,

LM> I'm trying to calculate Hirshfeld charges as a postprocess. To do so,
LM> I need to obtain the atomic rho for each atom, in real space. I've
LM> seen that "atomic_rho.f90" calculates the total rho as a superposition
LM> of the individual atomic ones, obtained from the pseudopotentials.
LM> But I couldn't understand how this superposition is done, as the
LM> internal loop is based on atomic types, and not on individual atoms. I

well, for practical reasons it is more efficient to loop over
atom types and atoms per atom type. per atom-type parameters 
only need to be computed once this way.

LM> couldn't also find how the atomic coordinates are used (to "center"
LM> the charge on the atomic position), and which variable stores them. I
LM> saw that it was all done in reciprocal space, and probably this is
LM> where I'm confusing myself.

i suggest you first have a look into textbook material 
explaining the implementation of electronic structure
calculation with plane wave pseudopotentials (e.g. the 
books by jorge kohnoff or richard martin). and then
read the marx / hutter review which also gives an overview
on how the implementation can be done (on the example of
the CPMD code, which is not that different as far as the 
basic principles are concerned). the CPMD code actually 
does have an implementation of hirshfeld charges determination, 
but only for norm-conserving pseudopotentials, IIRC, so you
can look up how the implementation principles.

for implementing it into QE you'll have to figure out
how to handle ultra-soft psps contribution to the atomic
density on top of everything else.

good luck,
   axel.


LM> Can someone please give me a hand?
LM> 
LM> Thanks,
LM> 
LM> Leonardo Matheus
LM> Doctorate student - Physics Institute, University of São Paulo, Brazil
LM> Nanomol group - http://nanomol.if.usp.br
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LM> 

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