[DFTB-Plus-User] anion+cation systems

[Bálint Aradi]

Dear Alexey,

> Is it possible to calculate a molecular dimer where charges are 
> separated (anion + cation)? Like C60(1-) and K+ system.
> Which *.hsd file should be in this case?
> I've read about  CustomisedOccupation option but didn't clearly undetand 
> how to add exactly one excessive electron to whole molecule.

The problem is, that although you have two molecules in the same system, 
you will have one global Fermi-level. So, depending on the alignment of 
the energy levels in the two systems, you may experience "artificial" 
charge transfer between them. Setting any kind of initial occupation 
won't really help, because after the first diagonalization the global 
energy levels would be filled up according to the filling function. As 
far as I know (I am defintitely not the expert for it), the transfer 
effect is usually more prominent with GGA (e.g. mio/3ob set) and much 
less severe with range separated functionals (ob2-set).

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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