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Dear Christopher,
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<div class="">A few comments.</div>
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<div class="">- Which pseudo are you using? Also, the cutoff might need to be increased (I imagine what you state is the wfc cutoff, what about the charge density cutoff?)</div>
<div class="">E.g. in the link Nicola sent, they use 56/219 as cutoffs, with SSSP pseudos <a href="https://molmod.ugent.be/sites/default/files/deltadftcodes/supplmat/SupplMat-QE-SSSP-acc.pdf" class="">https://molmod.ugent.be/sites/default/files/deltadftcodes/supplmat/SupplMat-QE-SSSP-acc.pdf</a></div>
<div class="">And also the k-mesh density they use is of 20x20x20 (if they used it probably it’s a good indication you might need to go to that convergence to ensure that you results are correct)</div>
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<div class="">- more generally, it would be easier and you wold get faster feedback if you could share your calculation inputs and outputs, and a detail of how you computed the constants</div>
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<div class="">- in the link that Nicola provided, if you check the PDF for the “best" QE and VASP calculations (the one with smaller delta w.r.t. a full-electron code, wien2k in this case), you will find the values of B0 and B1, namely for Silicon</div>
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<div class="">B0=88.698 GPa, B1=4.318 [QE, link above]</div>
<div class="">B0=88.753 GPa, B1=4.297 [VASP: <a href="https://molmod.ugent.be/sites/default/files/deltadftcodes/supplmat/SupplMat-VASP2015GW.pdf" class="">
https://molmod.ugent.be/sites/default/files/deltadftcodes/supplmat/SupplMat-VASP2015GW.pdf</a>]</div>
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<div class="">This shows that VASP and QE are in very good agreement.</div>
<div class="">Also, considering that for cubic systems B0 = (c11 + 2*c12)/3, if I’m not mistaken from the numbers you report you would get (for B0) 83.3 for VASP, 93.3 for QE.</div>
<div class="">As I tend to believe that the one published at the links are converged, I think this means that both your reference data from the Materials Project and your simulations still are not fully converged. (As a note in passing, this also shows that
we shouldn’t always believe that all data from online databases is always well converged - especially if you cannot check the exact inputs and input parameters that they used.)</div>
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<div class="">If you redo the simulations with more converged parameters and you still have discrepancies (from the values from the molmod link), I suggest that you send us the calculation details (as I mention above) so that we can investigate more.</div>
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<div class="">Best,</div>
<div class="">Giovanni</div>
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-- <br class="">
Giovanni Pizzi<br class="">
Theory and Simulation of Materials and MARVEL, EPFL<br class="">
<a href="http://people.epfl.ch/giovanni.pizzi" class="">http://people.epfl.ch/giovanni.pizzi</a><br class="">
http://nccr-marvel.ch/en/people/profile/giovanni-pizzi</div>
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<div class="">On 12 Feb 2019, at 22:28, Christopher Pashartis (----) <<a href="mailto:Christopher.Pashartis@imec.be" class="">Christopher.Pashartis@imec.be</a>> wrote:</div>
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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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<font face="Calibri, sans-serif" style="font-size: 11pt;" class=""><b class="">From:</b><span class="Apple-converted-space"> </span>Nicola Marzari <<a href="mailto:nicola.marzari@epfl.ch" class="">nicola.marzari@epfl.ch</a>><br class="">
<b class="">Sent:</b><span class="Apple-converted-space"> </span>Tuesday, February 12, 2019 9:18 PM<br class="">
<b class="">To:</b><span class="Apple-converted-space"> </span>General discussion list for Quantum ESPRESSO developers; Christopher Pashartis (----)<br class="">
<b class="">Subject:</b><span class="Apple-converted-space"> </span>Re: [QE-developers] Significant Deviations from Elastic Tensors from existing codes</font>
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Dear Christopher,<br class="">
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thanks for reporting, but no bug - QE and VASP (if you use GW-ready<span class="Apple-converted-space"> </span><br class="">
pseudo) have actually the best agreement of bulk moduli with all-<br class="">
electron codes:<span class="Apple-converted-space"> </span><a href="https://molmod.ugent.be/deltacodesdft" class="">https://molmod.ugent.be/deltacodesdft</a><br class="">
<br class="">
Discrepancies between codes are due to different pseudopotentials or the<span class="Apple-converted-space"> </span><br class="">
numerically details needed to get a well converged calculation - not<span class="Apple-converted-space"> </span><br class="">
trivial, at al: it depends if you are fitting the energy or the stress,<br class="">
how much strain you are using, superconvergence on cutoffs, kpoints and<span class="Apple-converted-space"> </span><br class="">
selfconsistency - hence why most values in the literature are poorly<span class="Apple-converted-space"> </span><br class="">
converged, and properly done calculations, as those in the link above,<br class="">
agree very closely.<br class="">
<br class="">
nicola<br class="">
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On 12/02/2019 07:49, Christopher Pashartis (----) wrote:<br class="">
> Dear Developer(s),<br class="">
><span class="Apple-converted-space"> </span><br class="">
> I have encountered what would appear to be a serious bug in your code. I<span class="Apple-converted-space"> </span><br class="">
> have been trying to tabulate some elastic constants for Si and Cu only<span class="Apple-converted-space"> </span><br class="">
> to realize that your code has some issues with some components of the<span class="Apple-converted-space"> </span><br class="">
> elastic tensor.<br class="">
><span class="Apple-converted-space"> </span><br class="">
> Namely, the c44 component of Si and c11 component of Cu. All my other<span class="Apple-converted-space"> </span><br class="">
> parameters are within a reasonable range of existing VASP calculations.<br class="">
><span class="Apple-converted-space"> </span><br class="">
> For example Si (in GPa):<br class="">
> Component<br class="">
> Materials Project (VASP)<br class="">
> ESPRESSO with the same routine as Materials Project (I did these calcs)<br class="">
> c11<br class="">
> 144<br class="">
> 156<br class="">
> c12<br class="">
> 53<br class="">
> 62<br class="">
> c44<br class="">
> 75<br class="">
> 104<br class="">
><span class="Apple-converted-space"> </span><br class="">
> I have converged my cutoff parameters and kpoint mesh. I also tried<span class="Apple-converted-space"> </span><br class="">
> fiddling with the tolerances on energy and forces./*All of these are<span class="Apple-converted-space"> </span><br class="">
> converged in the values I show you above*/.It would seem both your<span class="Apple-converted-space"> </span><br class="">
> energies and forces are miscalculated in certain deformation directions<span class="Apple-converted-space"> </span><br class="">
> (and no I did not apply too much of a deformation). I am fairly certain<span class="Apple-converted-space"> </span><br class="">
> that these issues have nothing to do with my code as I also implemented<span class="Apple-converted-space"> </span><br class="">
> it for CP2k and the results were within acceptable margins of existing code.<br class="">
><span class="Apple-converted-space"> </span><br class="">
> If you require any more information to assist you in this effort, let me<span class="Apple-converted-space"> </span><br class="">
> know.<br class="">
><span class="Apple-converted-space"> </span><br class="">
> *CHRISTOPHER PASHARTIS*<br class="">
><span class="Apple-converted-space"> </span><br class="">
> PhD Student in Computational Materials<br class="">
><span class="Apple-converted-space"> </span><br class="">
> <a href="mailto:christopher.pashartis@imec.be" class="">christopher.pashartis@imec.be</a><<a href="mailto:christopher.pashartis@imec.be" class="">mailto:christopher.pashartis@imec.be</a>>I_www.imec.be_<<a href="http://www.imec.be/" class="">http://www.imec.be/</a>><br class="">
><span class="Apple-converted-space"> </span><br class="">
> Kapeldreef 75I3001 LeuvenIBelgium<br class="">
><span class="Apple-converted-space"> </span><br class="">
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> _______________________________________________<br class="">
> developers mailing list<br class="">
> <a href="mailto:developers@lists.quantum-espresso.org" class="">developers@lists.quantum-espresso.org</a><br class="">
><span class="Apple-converted-space"> </span><a href="https://lists.quantum-espresso.org/mailman/listinfo/developers" class="">https://lists.quantum-espresso.org/mailman/listinfo/developers</a><br class="">
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<br class="">
--<span class="Apple-converted-space"> </span><br class="">
----------------------------------------------------------------------<br class="">
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL<br class="">
Director, National Centre for Competence in Research NCCR MARVEL, EPFL<br class="">
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