[CP2K-user] [CP2K:21309] MoS2 in CP2K and CPMD: identical models give different results

[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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