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Hello Nicola,</div>
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I am aware of many of the items you have stated. If you could show me a calculation of the Elastic Tensor with ESPRESSO for Si I would be more inclined to believe that ESPRESSO is not at fault. I tested different pseudopotentials, it didn't help ESPRESSO's
case. I did converge to what I thought was an appropriate cutoff and kpoint mesh (I believe I used 30Ry and 11x11x11, comparable to materials project parameters used in VASP).</div>
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Again, perhaps just a thought from me, it could be due to breaking the symmetry of the crystal as is the case when you apply a deformation.</div>
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I will get back to you as soon as I can with more information. On the meantime, it might be nice if one of you can do a calculation with ElaStic to what you may believe would be overconverged values.</div>
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P.S. Unless I am missing the point, I fail to see how the link you showed me affects the elastic tensor.</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Nicola Marzari <nicola.marzari@epfl.ch><br>
<b>Sent:</b> Tuesday, February 12, 2019 9:18 PM<br>
<b>To:</b> General discussion list for Quantum ESPRESSO developers; Christopher Pashartis (----)<br>
<b>Subject:</b> Re: [QE-developers] Significant Deviations from Elastic Tensors from existing codes</font>
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Dear Christopher,<br>
<br>
<br>
thanks for reporting, but no bug - QE and VASP (if you use GW-ready <br>
pseudo) have actually the best agreement of bulk moduli with all-<br>
electron codes: <a href="https://molmod.ugent.be/deltacodesdft">https://molmod.ugent.be/deltacodesdft</a><br>
<br>
Discrepancies between codes are due to different pseudopotentials or the <br>
numerically details needed to get a well converged calculation - not <br>
trivial, at al: it depends if you are fitting the energy or the stress,<br>
how much strain you are using, superconvergence on cutoffs, kpoints and <br>
selfconsistency - hence why most values in the literature are poorly <br>
converged, and properly done calculations, as those in the link above,<br>
agree very closely.<br>
<br>
nicola<br>
<br>
<br>
<br>
<br>
On 12/02/2019 07:49, Christopher Pashartis (----) wrote:<br>
> Dear Developer(s),<br>
> <br>
> I have encountered what would appear to be a serious bug in your code. I <br>
> have been trying to tabulate some elastic constants for Si and Cu only <br>
> to realize that your code has some issues with some components of the <br>
> elastic tensor.<br>
> <br>
> Namely, the c44 component of Si and c11 component of Cu. All my other <br>
> parameters are within a reasonable range of existing VASP calculations.<br>
> <br>
> For example Si (in GPa):<br>
> Component<br>
> Materials Project (VASP)<br>
> ESPRESSO with the same routine as Materials Project (I did these calcs)<br>
> c11<br>
> 144<br>
> 156<br>
> c12<br>
> 53<br>
> 62<br>
> c44<br>
> 75<br>
> 104<br>
> <br>
> I have converged my cutoff parameters and kpoint mesh. I also tried <br>
> fiddling with the tolerances on energy and forces./*All of these are <br>
> converged in the values I show you above*/.It would seem both your <br>
> energies and forces are miscalculated in certain deformation directions <br>
> (and no I did not apply too much of a deformation). I am fairly certain <br>
> that these issues have nothing to do with my code as I also implemented <br>
> it for CP2k and the results were within acceptable margins of existing code.<br>
> <br>
> If you require any more information to assist you in this effort, let me <br>
> know.<br>
> <br>
> *CHRISTOPHER PASHARTIS*<br>
> <br>
> PhD Student in Computational Materials<br>
> <br>
> christopher.pashartis@imec.be<mailto:christopher.pashartis@imec.be>I_www.imec.be_<http://www.imec.be/><br>
> <br>
> Kapeldreef 75I3001 LeuvenIBelgium<br>
> <br>
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> _______________________________________________<br>
> developers mailing list<br>
> developers@lists.quantum-espresso.org<br>
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<br>
-- <br>
----------------------------------------------------------------------<br>
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL<br>
Director, National Centre for Competence in Research NCCR MARVEL, EPFL<br>
<a href="http://theossrv1.epfl.ch/Main/Contact">http://theossrv1.epfl.ch/Main/Contact</a>
<a href="http://nccr-marvel.ch/en/project">http://nccr-marvel.ch/en/project</a><br>
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