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

[L Heidarizadeh]

Hi Marcella,
Thank you for your feedback and suggestions. I wanted to update you on what 
I’ve tried so far and ask for some additional guidance.
Since I didn’t include a &KPOINTS block, CP2K defaulted to Γ-point-only 
sampling. For my 2x2x1 periodic system, I realize this might not be 
sufficient, especially for accurate TDDFT calculations. should I add a 2 × 
2 × 1 k-point grid to sample the Brillouin zone more effectively?

For MD simulations, I’ve been using Γ-point-only sampling since the focus 
is on atomic forces. Would you recommend defining a small k-point grid 
(e.g., 2 × 2 × 1) for MD runs as well, or is Γ-point-only sufficient in 
this case?

I increased the energy cutoff to 500 Ry but still faced convergence issues 
with the surface model. I also adjusted the mixing parameter ALPHA down to 
0.005, but the issue persisted.
I also applied DFT+U  However, I’m still encountering issues with the 
surface convergence.

I tried adding a sulfur layer and hydrogen passivation to address dangling 
bonds, but the SCF still failed to converge. You mentioned surface 
reconstruction—would you suggest running a geometry optimization on the 
surface before attempting SCF calculations? Also, are there any specific 
techniques or guidelines for identifying and capping dangling bonds 
effectively to stabilize the surface?

I really appreciate your insights so far. If you have any further 
recommendations, I would be grateful.

Best regards,
Layla

On Thursday, October 17, 2024 at 4:17:58 AM UTC-4 Marcella Iannuzzi wrote:

> 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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