<div>Dear <span> Nikita </span><span>Fominykh,</span></div><div><span><br /></span></div><div>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.</div><div><br /></div><div>Best regards</div><div>Martin Konôpka.</div><br /><div class="gmail_quote"><div dir="auto" class="gmail_attr">Dátum: piatok 28. marca 2025, čas: 18:13:13 UTC+1, odosielateľ: Fominykh Nikita<br/></div><blockquote class="gmail_quote" style="margin: 0 0 0 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">Dear colleagues,<br><br>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.<br><br>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.<br><br>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.<br><br>In order to decipher the puzzle, I have made calculations for pure Mo and for pure S.<br><br>2) For the bcc Mo structure all the codes with different pseudopotentials give very close results.<br><br>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. <br><br>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. <br><br>There are example files for these comparisons attached. <br><br>Please let me know your best judgement about the possible roots of these discrepancies.<br><br>Best regards,<br>Nikita<br></blockquote></div>
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