Fixing positions of multiple atoms with different constraints

[Rafael Soler-Crespo]

Hi all,

I am trying to do a calculation in which I fix the edges of a sheet 
(graphene) with different boundary conditions. The calculation is a 
geometry optimization. The left and right ends of the sheet are constrained 
to not move in the x direction. The top and bottom parts of the sheet are 
constrained to not move in the y direction. However, due to how the 
FIXED_ATOMS section works in CP2K I cannot create different constraints for 
each end of the sheet (in other words, I am forced to use a global 
constraint which I do not want). Does anyone know any way to get around 
this?

For example, I would like to do:

   LIST                                1 2 3 4
   COMPONENTS_TO_FIX    XY
   LIST                                 5 6 7 8
   COMPONENTS_TO_FIX    YZ

However, the code won't let me do that (the keywords appear twice).

Any help will be greatly appreciated.

Thanks,
Rafael
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