[CP2K-user] [CP2K:21471] Clarification on k-point sampling, slab passivation, and convergence in CP2K

[usman ul muazzam]

Dear CP2K Users and Developers,

I am trying to model *Ga and O adatom diffusion barriers* on substrates 
like *diamond and sapphire* using CP2K (periodic DFT + NEB), and I have a 
few questions regarding best practices:

*1. k-point Sampling:*
Some CP2K publications seem to use *only Gamma-point*, even for periodic 
systems. In contrast, codes like Quantum ESPRESSO require k-point 
convergence for accuracy.

   - 
   
   Is k-point convergence generally *not needed* in CP2K.
   - 
   
   When should one use explicit *k-point grids* in CP2K.
   
*2. Slab Model Passivation:*
In plane-wave codes, bottom surface passivation (e.g., with hydrogen) is 
common in slab models to avoid spurious states. But I rarely see this in 
CP2K-based surface studies.

   - 
   
   Is *bottom-layer passivation not necessary* in CP2K.
   
*3. Convergence Parameters:*
Is optimizing *CUTOFF* and *REL_CUTOFF* typically *sufficient* for accurate 
periodic DFT and NEB calculations in CP2K.

   - 
   
   Are other parameters like *basis sets (as here we use Gaussian instead 
   of plane wave)* or *grid levels* also important to converge.
   - 
   
   Any recommended references for CP2K convergence strategies.
   
Any guidance or pointers to best practices would be greatly appreciated.


Best Regards,

Usman

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