[DFTB-Plus-User] Question on Background Charge Effects in Fixed-Charge Simulations

[Bálint Aradi]

Dear Kazem,

Please note, that there is no |TotalCharge| option in DFTB+. The total 
charge of the system is controlled by the |Charge| option in the 
|Hamiltonian| block (and not in |Driver| as you assumed!).

Similar to other atomistic simulation codes, also DFTB+ calculates the 
charge-charge interaction in *periodic* systems via the Ewald summation, 
leaving away the singular g=0 term in the reciprocal part of the 
summation. In case of charged systems, this implicitly leads to the 
introduction of a compensating jellium, with all its consequences. Note, 
that this only happens in periodic systems, in non-periodic systems 
(clusters) no jellium is introduced.

Best regards,

Bálint

On 7/29/25 12:31 PM, Zhour, Kazem wrote:
> Hello,
> 
> When applying a fixed total charge to a system (e.g., via |TotalCharge| 
> in the |Driver| block), can we assume that the resulting adsorption 
> energies are free from spurious effects caused by background charge 
> compensation?
> 
> I am particularly interested in whether DFTB+ introduces any implicit 
> uniform background charge or electrostatic correction in such charged 
> calculations, and if so, whether it impacts total energy differences 
> such as adsorption energies.
> 
> I would appreciate any clarification or guidance on this.
> 
> Best regards,
> 
> Kazem
> 
> 
> 
> 
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-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.uni-bremen.de/en/lmcqm/b-aradi

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