[CP2K-user] NEB for diffusion energy barriers

[Stefano Ferrero]

Dear CP2K experts,

I have just started using CP2K and I would be really thankful if anybody 
can help me.
I am trying to calculate diffusion barriers of single atoms adsorbed on a 
surface using the NEB method.
I optimized at DFT level the initial and final positions of the diffusion 
hop and I am providing those as first and last replicas.
I have some questions about the set up of the calculation and the 
computational strategy to follow to obtain good results.

1) My system contains more than 200 atoms. Can I fix the atoms underneath 
the first layer of the surface to save computational time?
2) Should the value of K_SPRING be varied in order to see if there are 
changes in the results?
3) Should the value of NUMBER_OF_REPLICAS be varied in order to see if 
there are changes in the results?
4) Are there any other important parameters to take care of?
5) When plotting the energy profile of the NEB calculations I always find 
that the last frame, which I gave as an input, changes in energy with 
respect to the result found in the geometry optimization previously 
performed.Is it due to the ALIGN_FRAMES and ROTATE_FRAMES keywords, which I 
did not switched off? 

Is this a good strategy to obtain the diffusion energy barriers or would 
you suggest something else?

I've attached the input file used and the geometries of the initial and 
final replicas.
Thank you for your help!

Stefano Ferrero
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