[CP2K-user] [CP2K:21310] Re: MoS2 in CP2K and CPMD: identical models give different results

[Martin Konôpka]

Dear Nikita Fominykh,

The differences may be because of the quite different basis sets used in 
CP2K/Quickstep on one side and in CPMD and VASP on the other side. I mean 
basis sets for wavefunctions. In CP2K the standard method is to use 
gaussian basis sets (and you really used them). In CPMD and VASP plane-wave 
basis sets are used.

Best regards
Martin Konôpka.

Dátum: piatok 28. marca 2025, čas: 18:13:13 UTC+1, odosielateľ: Fominykh 
Nikita

> Dear colleagues,
>
> I am comparing the MoS2 model with the PBE xc-functional in CP2K and CPMD 
> with the same GTH pseudopotential. I have found some strange discrepancies.
>
> For comparison, I calculate energy differences while changing the lattice 
> constant in the xy-plane (compression and tension). In these tests I use 
> Gamma point only. Please see 3 plots with the Energy-vs-Strain attached.
>
> 1) First, let us consider the bulk MoS2 in the 2H structure. CP2K and CPMD 
> with the same GTH pseudopotential give different results. Other CPMD 
> calculations with the ‘CPMD-native’ GTH model and the CPMD MT 
> pseudopotential give similar results to CPMD-withGTHcp2k. Interestingly, 
> VASP results are very close to CP2K.
>
> In order to decipher the puzzle, I have made calculations for pure Mo and 
> for pure S.
>
> 2) For the bcc Mo structure all the codes with different pseudopotentials 
> give very close results.
>
> 3) However, for the S6 structure of sulphur, the CPMD-withGTHcp2k and 
> CPMD-withMT results agree well with VASP, but do not match CP2K. And the 
> CPMD results for its ‘native’ GTH model show a significant offset. 
>
> I also tried changing energy cutoffs, enabling various k-meshes, and 
> enlarging the cell, however I couldn’t find the possible reasons for these 
> discrepancies in CP2K and CPMD with the same GTH pseudopotential of MoS2 
> and for S6. 
>
> There are example files for these comparisons attached. 
>
> Please let me know your best judgement about the possible roots of these 
> discrepancies.
>
> Best regards,
> Nikita
>

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