[Pw_forum] Charge difference query

[Axel Kohlmeyer]

On Tue, 17 Jul 2007, Kenneth Wong wrote:

KW> Dear PWscf,

dear ken,

KW> I wish to get some help regarding the calculation of the charge difference.
KW> For example, if H2O was adsorbed onto TiO2 i want to see the charge
KW> difference this is how i would go about it
KW> 
KW> Charge density of
KW> a. (H2O + TiO2)
KW> b. (TiO2)
KW> c. (H2O)
KW> Charge density difference =  a - (b+c)
KW> 
KW> So i would save the the a, b, c, intermediate files all in e.g.
KW> separate calculation

the following is just what i gathered from reading the
documentation. so it may or may not work, but at least
it should put you into the right direction...
 
KW> &inputPP
KW> filplot='inter(1)'

this would be the output file name: 'densdiff'

                           ...........then 'inter(2) then 'inter(3)'

nope.

KW> (i guess they will all have to be in different names? inter(1), inter(2),
KW> inter(3) as a, b, c, respectively)
KW> 
KW> Now, here is where i am lost.....
KW> &plot
KW> nfile = 3
KW> filepp(3)=inter,

here you provide 3 array element for input file and weights.

filepp(1)='h2o_plus_tio2'
filepp(2)='h2o'
filepp(3)='tio2'

KW> weight(3) =weight(1)*rho(1)  -  ( weight(2)*rho(2)+weight(3)*rho(3)),

weight(1)=1.0
weight(2)=-1.0
weight(3)=-1.0

that should give you what you want. the postprocess job will just
loop over all files, pick the desired property and sum it after 
multiplying with the weight into the result data and finaly write
it out in the desired format.
does that make sense to you?

cheers,
   axel.

KW> 
KW> i don't know what to do in this section, in regards to how to use weight(i),
KW> filepp(i)
KW> 
KW> 
KW> Thank you very much,
KW> 
KW> regards, Ken.
KW> 

-- 
=======================================================================
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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If you make something idiot-proof, the universe creates a better idiot.