[CP2K-user] [CP2K:12909] What are the ways to add a charge to a system?

[Patrick Gono]

Dear Devyesh,

The CHARGE keyword manages the total charge of the simulated system. For
example, CHARGE -1 increases the number of electrons by one. Unfortunately,
you can't really know where the electron decides to localize, if at all.
You can modify your starting geometry to make the structure more conducive
to the behavior of the extra charge you want to see. For instance, you
could increase or decrease the bond length in your charged simulations.

You can also modify the core charge of selected ions through the CP2K_INPUT
/ FORCE_EVAL / SUBSYS / KIND / CORE_CORRECTION keyword. For example, you
could try to put extra fractional charge on just the two ions forming the
bond. You can then optimize the structure, remove the CORE_CORRECTION and
add or subtract an electron by setting CHARGE appropriately. This way, the
extra charge should, in principle, move to the bond you wish to study.

Finally, you can also take a look at constrained DFT, which allows you to
enforce constraints on the electronic density:
https://www.cp2k.org/howto:cdft

Yours sincerely,
Patrick Gono

On Fri, 21 Feb 2020 at 23:45, Dev Rana <dev.... at gmail.com> wrote:

> I was looking to put a charge to a C-Al bond. Specifically if there was a
> C+ or a C- to the molecule.
>
> C+ -- Al
> C -- Al
> C- -- Al
>
> Does anyone know how I would go about this?
>
> Is it as simple as using Force_Eval > DFT > Charge 0, -1, +1?
>
> Best Regards,
> Devyesh Rana
>
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