[CP2K-user] [CP2K:21318] MoS2 in CP2K and CPMD: identical models give different results

[Nikita Fominykh]

Dear Dr. Konôpka, dear Prof. Hutter, 

thank you very much for the helpful hints! After additional tests with the 
plane wave Sirius implementation, I could find the following answers:

1) In the case of pure S the problem was really in the basis. So with 
Sirius, it was possible to get an immediate agreement. When I picked 
TZV2PX, I got the agreement with Quickstep too.

2) In the case of MoS2, where I initially checked the convergence of the 
basis, it turned out to have no significant impact. 

However, in further tests I noticed a difference in the electrostatic 
energies. To reproduce the results from CP2K in CPMD, it turned out to be 
necessary to increase the number of additional supercells included in the 
real space sum for the Ewald term (the TESR was zero by default).

Best regards,

Nikita


понедельник, 31 марта 2025 г. в 13:05:04 UTC+3, Jürg Hutter: 

> Hi
>
> I see (or guess) two possible problems:
>
> 1) The GTH PP for S from CPMD is not good. You could check this by running 
> that PP in CP2K.
> 2) GTH PP in CPMD need a high cutoff. Your CPMD(GTH) calculation is not 
> yet converged?
>
> regards
> JH
>
> ________________________________________
> From: cp... at googlegroups.com <cp... at googlegroups.com> on behalf of 
> Fominykh Nikita <nikfo... at gmail.com>
> Sent: Friday, March 28, 2025 6:13 PM
> To: cp2k
> Subject: [CP2K:21309] MoS2 in CP2K and CPMD: identical models give 
> different results
>
> 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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