[CP2K-user] How does work on the EXTERNAL_POTENTIAL

[Marcella Iannuzzi]

Dear Ning, 

It is a very simple potential, which is zero at the center of the Cartesian 
system, and grows as a power 4 of the square of the atomic coordinates, 
with a very small prefactor.
 Just plot it to see how it grows and in which range it is negligibly small.
This definition assumes that the molecular system is centred at 0, and it 
is not extending beyond the range where the potential is still negligible.
Regards,
Marcella

On Monday, December 16, 2019 at 3:44:46 PM UTC+1, ning zhang wrote:
>
> Hi Everyone,
>
> I am learning the metadynamics by the website: 
> https://www.cp2k.org/exercises:2015_cecam_tutorial:mtd1
>
> However, there is a question on the CP2K_INPUT 
> <https://manual.cp2k.org/trunk/CP2K_INPUT.html>/FORCE_EVAL 
> <https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL.html>/
> EXTERNAL_POTENTIAL 
> <https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/EXTERNAL_POTENTIAL.html>. 
> In the first task of tutorial, an example on the dynamics of two HNO3 
> molecules over a graphene sheet are considered. If a constraint is not 
> added, it is observed that the two molecules very fast and expolre a large 
> spece of configurations, being often far from each other and far from 
> graphene. In order to restrict the exploration to region, it is necessary 
> to limit the movement of the two molecules. To this purpose, an external 
> potential defining a spherical potential centered on the center of the 
> system coordinated is added. The potential is given as follows:
>
>  &EXTERNAL_POTENTIAL
>      ATOMS_LIST   61..70
>      FUNCTION   0.000000000001*(Z^2)^4
>   &END
>
>   &EXTERNAL_POTENTIAL
>      ATOMS_LIST   61..70
>      FUNCTION   0.0000000000001*(X^2)^4
>   &END
>
>   &EXTERNAL_POTENTIAL
>      ATOMS_LIST   61..70
>      FUNCTION   0.0000000000001*(Y^2)^4
>   &END
>
>
> Question: How does work on such external_potential? i.e., How does such 
> external_potential constaint the two HNO3 molecules to the vicinity 
> of graphene?
>
> Ning
>
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