[DFTB-Plus-User] Charge density with DFTB+

[Bálint Aradi]

Dear Daniele,

> It is possible to have a real charge density (rho) of the system?

Yes, for example waveplot is able to render the charge density of the
system on a grid, if needed. You typically do it a posteriori, though.

> I would like my system to interact with external point charges, 
> but, as far as I have understood, the coulomb interaction term is 
> between the Mulliken charges of the system and the external point 
> charges. Usually, in standard DFT, you would have an interaction between 
> the charge density (rho) of the system and the external point charges.

The big advantage of DFTB over DFT is speed, and parts of this speed
advantage come from the simplified charge model. Using the explicit
spatial-dependent density during the calculation is technically
possible, but slow things down considerably, so it is questionable,
whether it is worth the effort.

> If this is not the case, it would be possible to have other charges
> (better than 
> the Mulliken one) from DFTB+?

Depending who you ask, the answer may be different. In my opinion,
though, the Mulliken charges are the natural choice for being the basis
of the electrostatics in DFTB.

Is there any special reason, why the Mulliken-charges are not
satisfactory for your purpose?

  Best regards,

  Bálint

-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.bccms.uni-bremen.de/cms/people/b-aradi/


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