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

[Dev Rana]

Hi Patrick!

Thank you so much for your very thorough response. This absolutely answers 
my question on how to do this. I was trying to avoid having a "globally" 
charged system i.e. having an electric field, and I believe this does just 
that. I'm comparing this data directly with a simulation of block of Al and 
C and the output radial distribution function (RDF), with the aim being to 
see if there's a bond forming. I was specifically trying to compare the 
bond length of a simple Al-C system (neutral or charged ions) and see if 
that bond length that results corresponds to the RDF data. 

Thank you for this! Have a great weekend!

Best Regards,
Devyesh Rana

On Saturday, February 22, 2020 at 6:22:06 AM UTC-5, Patrick Gono wrote:
>
> 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 <d... at gmail.com <javascript:>> 
> 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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