[CP2K-user] [CP2K:20777] Re: SCF Convergence Issues with OT and Diagonalization for CZTS System (Vacuum, Sulfur Layer, and Hydrogen Passivation

[Marcella Iannuzzi]

Hi ...

It is good that the bulk system converges. Do you also obtain the correct 
electronic structure? The energy cutoff seems very low. 
Are you using k-points for the bulk?  Is the PBE functional good enough for 
this type of systems?  12 grids are too many, just use 4 or 5

I suppose that depending on how you cleave the bulk, there might be 
dangling bonds that should be saturated.
Maybe the surface needs to go through a reconstruction (just guessing), in 
this case it might help to adjust the coordinates to avoid too many 
dangling bonds.

Diagonalization is recommended if the energy gap is very small, which can 
be the case if you have unrelaxed dangling bonds at the surface.
In this case, a smaller mixing ALPHA parameter might help, like 0.005.

Regards
Marcella



 


On Wednesday, October 16, 2024 at 11:57:41 PM UTC+2 lheid... at gmail.com 
wrote:

> Hi,
>   Thank you for the suggestion! I’ve already tested the *bulk CZTS system* 
> with the same *basis sets, pseudopotentials, and exchange-correlation 
> functional*, and it *converged successfully*. However, the *convergence 
> problem arises only after introducing the 20 Å vacuum layer* and *surface 
> modifications*. I've Adjusted *MAX_SCF* values (up to 500 iterations) and 
> tried various *mixing parameters*, including Broyden mixing, but no 
> improvement. I have attached my input file for more clarification (before 
> switching to OT).
> Thank you again for your help and suggestions!
> Best regards,
> Layla
>
> On Wednesday, October 16, 2024 at 2:15:52 PM UTC-4 Marcella Iannuzzi wrote:
>
>>
>> Hi ..
>>
>> Maybe it simply needs to run for more iterations to converge.
>> With the information you provide it is hard to guess.
>> Is the electronic structure calculation of the bulk working fine?
>> Can you reproduce with your settings (BS, PP, XC etc) the known bulk 
>> properties?
>>
>> Regards
>> Marcella
>>
>>
>>
>> On Wednesday, October 16, 2024 at 7:40:32 PM UTC+2 lheid... at gmail.com 
>> wrote:
>>
>>> Hello CP2K community,
>>>
>>> I am running molecular dynamics (MD) simulations on a *Cu2ZnSnS4 (CZTS)* 
>>> system using *DFT* in CP2K. Below is a detailed description of my 
>>> system and the modifications I applied, followed by the SCF convergence 
>>> issue I am facing.
>>>
>>> Cu2ZnSnS4 (CZTS) system modeled in a periodic box.
>>> Unit cell dimensions: 10.8 × 10.8 × 10.8 Å.
>>> The goal is to study surface interactions and electronic properties with 
>>> a vacuum layer.
>>>
>>> A 20 Å vacuum layer was added in the Z direction to simulate surface 
>>> effects: 10.8 × 10.8 × 30.8 Å
>>>
>>> A layer of sulfur (S) atoms was added to the surface to stabilize the 
>>> system and account for surface states.
>>>
>>> I attempted hydrogen passivation by capping the dangling bonds with H 
>>> atoms to further stabilize the surface.
>>> I tried running the SCF loop with and without hydrogen passivation, but 
>>> both cases failed to converge.
>>>
>>> SCF Settings and Methods Tried:
>>> *Orbital Transformation (OT):*
>>> MINIMIZER: DIIS
>>> PRECONDITIONER: FULL_SINGLE_INVERSE
>>> ENERGY_GAP: 0.001
>>> N_HISTORY_VEC: 7
>>> *Diagonalization:*
>>> I disabled the OT section and enabled diagonalization as a fallback 
>>> method, but the SCF still did not converge. ( I tried different parameters 
>>> setting)
>>> SCF Parameters:
>>> SCF_GUESS: ATOMIC
>>> EPS_SCF: 1.0E-6
>>> MAX_SCF: 100
>>>
>>> *The SCF loop exits after a few minutes, failing to converge under both 
>>> OT and diagonalization methods.*
>>> Are there specific SCF settings or preconditioners that can improve 
>>> convergence for systems with large vacuum gaps?
>>> Are there alternative strategies for handling surfaces and vacuum layers 
>>> that could make the system more stable for electronic structure 
>>> calculations?
>>> Has anyone successfully applied hydrogen passivation to stabilize 
>>> surfaces and improve SCF convergence in CP2K?
>>>
>>> Any suggestions or advice would be greatly appreciated!
>>>
>>> Thank you for your help and support.
>>>
>>>
>>>

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