[CP2K-user] Stillinger cluster criterion in GEMC simulations

[Even Marius Nordhagen]

Dear CP2K experts,

I am currently trying to reproduce this article 
<https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.9b06348> [1], where the 
authors use Monte Carlo simulations, and AVBMC steps in particular, to 
build a water cluster from an (ideal) water reservoir. 

Since CP2K is the only freely available package that I could find with 
AVBMC implemented, I decided to give it a try. In other words, I am new to 
the package. 

In the gas reservoir there is no force between the molecules. In the box 
where the water cluster is being built, the molecules are interacting with 
a force-field (e.g. TIP3P). Only particles that belong to the cluster 
should be accepted. We define a maximum allowed distance between the 
particles in a cluster: If the distances between a particle A and all 
particles in a cluster is larger than this maximum distance, the particle A 
does not belong to the cluster (Stillinger cluster criterion). When moving 
particles from the reservoir to the cluster, we want to reject all moves 
where a particle is not being attached to the cluster.

So here comes my main question: Is it possible to define such an acceptance 
criterion in CP2K?

I started from the CP2K GEMC tutorial <https://www.cp2k.org/howto:gemc>[2], 
but cannot find a way to continue. I also have a question about the output 
files. The trajectory files for the two boxes are both written to the file 
mc_coordinates. When visualizing it in Ovito, it shows the two boxes every 
other frame. I want a trajectory file for each box. I tried this:

&MOTION
  &PRINT
    &TRAJECTORY ON
      FILENAME box1.trj
      FORMAT XYZ
    &END TRAJECTORY
  &END PRINT
&END MOTION

but no box1.trj file was written.

I appreciate any help I can get, I feel quite lost at the moment.

Links:
[1] https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.9b06348
[2] https://www.cp2k.org/howto:gemc

Best regards,
Even M. Nordhagen
PhD candidate in Computational Physics,
Department of Physics, University of Oslo
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