[DFTB-Plus-User] anion+cation systems

Ben Hourahine benjamin.hourahine at strath.ac.uk
Fri Mar 12 18:32:48 CET 2021


Hello Alexey,

the (DFTB) ground state may not necessarily be a state  with integer
charge transfer (it probably will not be), so standard  calculations
would not reproduce C60(1-) and K+ in that case. (Also, this may or may
not be the physical system, partly depending on how you define the
charge of the fragments but also the relative ionization and affinities
of the components).

There are a few ways to force such a charge transfer, but these are not
available in the current code base in an automated way. 1) a constrained
ground state calculation or 2) time propagation from isolated charged
fragments previously prepared in these charges. This case can be done
manually by performing separate calculations for C60(1-) and K(+) as
electron dynamics calculations, saving their states as an ascii file
(check WriteAsciiRestart in the manual). Then edit these files together
to make the composite system and restart from this. The electron
dynamics code will then propagate the system based on the charge
transfer fragments (I would suggest starting these as well separated
systems).

The 3ob set does contain potassium and carbon interactions (not sure how
well C60 would be simulated, so test it first).

Regards

Ben

On 11/03/2021 06:45, Alexey Kuzmin wrote:
>
> Dear developers,
>
> 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.
>
> Best regard,
> Alexey
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-- 
Dr.  B.  Hourahine,  Senior  lecturer
            SUPA, Department  of  Physics,
             University  of  Strathclyde,
              John  Anderson  Building,
          107 Rottenrow, Glasgow G4 0NG, UK.                    
  +44 141 548 2325, benjamin.hourahine at strath.ac.uk

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