[CP2K-user] [CP2K:21315] MoS2 in CP2K and CPMD: identical models give different results

[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: cp2k at googlegroups.com <cp2k at googlegroups.com> on behalf of Fominykh Nikita <nikfominyh 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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