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

[Marcella Iannuzzi]

Dear Stefano, 

1) You can fix atoms, but  this will not affect the computational time for the NEB simulation.

2) The default for K_SPRING is good in most of the cases. I would keep it unless you have a very good reason not to.

3) The NUMBER_OF_REPLICAS should be set such that the RMSD distance among neighbouring beads does not exceed 1-2 Å 

4) Be sure that you run on a total number of processors that is a multiple of NUMBER_OF_REPLICAS*NPROC_REP

5) This should be easy to check by comparing the absolute values of the coordinates. 

Kind regards,

Marcella

[Stefano Ferrero]

Dear Marcella,

Thank you very much for your help

Kind regards,

Stefano