[xcrysden] Difference charge density

[Tone Kokalj]

On Fri, 2013-07-19 at 17:39 +0530, Peram sreenivasa reddy wrote:
> Dear Tone,
>               Thank you very much for your reply. I want to know the
> flow from where to where?.  

It depends how you calculate your charge density difference.

> Is it from lower electro negativity element to higher electro
> negativity element. 

Usually that is so, yes. But what you see in charge density difference
plot depends how you calculate the difference. 

If you calculate it as a deformation density:

\delta\rho = \rho(system) - \sum_{i=1}^{natoms} \rho(atom_i)

then you may see what you proposed. 


But say you want to see a chemical bond between the fragment1 and
fragment2 in a system that is composed of fragment1+fragment2 (where
fragment means some group of atoms), then you may do:

\delta\rho = \rho(system) - \rho(fragment1) - \rho(fragment2)

where the geometries of system, fragment1, and fragment2 are kept
compatible.

So you see, what charge density difference shows depends on how it was
calculated.

Regards,
-- 
Anton Kokalj
J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia 
(tel: +386-1-477-3523 // fax:+386-1-477-3822)

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