<div dir="auto">Dear Lorenzo,<div dir="auto">Thankyou very much for providing the great help and information. Hopefully it will save lots of my time.</div><div dir="auto"><br></div><div dir="auto"><br><div data-smartmail="gmail_signature" dir="auto">Cheers!<br>Kiran</div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Nov 3, 2020, 19:16 Lorenzo Paulatto <<a href="mailto:paulatz@gmail.com" rel="noreferrer noreferrer" target="_blank">paulatz@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">> 1. Is there any procedure to know about nq values which will be okay to <br>
> get a phonon dispersion with reliable accuracy.<br>
<br>
Not really, usually 8x8x8 is enough for small systems (a couple of <br>
atoms), with 4x4x4 already being quite decent. For systems with a large <br>
unit-cell it could be even smaller. What you have to think, is the <br>
distance between atoms: computing a 4x4x4 grid is equivalent to using a <br>
4x4x4 supercell, is this large enough to have no interactions between <br>
periodic copies?<br>
<br>
> 2. Is there anything similar thing to do like we do a k-mesh convergence <br>
> test for scf calculation in order to get a reliable electronic band <br>
> structure.<br>
<br>
Yes, that is the ideal, you do a 2x2x2, then a 4x4x4 then a 6x6x6 and in <br>
every case you do a dispersion plot with q2r+matdyn, and see how much <br>
the points which are not in the original grid change. Unfortunately, <br>
ph.x does not reuse points from previous calculations (i.e. when doing <br>
the 4x4x4 after 2x2x2 some points are already available) but you can <br>
skip them by hand with some headscratching if you are so tight on cpu time.<br>
<br>
> 3. Is nq and nk grid similar ?<br>
<br>
They are both wavevectors of something in a crystal. In one case it is <br>
the electronic wavefunctions, in the other it is the monochromatic <br>
perturbation that we usually call "phonon".<br>
<br>
hth<br>
<br>
> <br>
> I tried to give all the information I could, I m new to QE so can't <br>
> explain my doubts better than this, so, please update whatever possible.<br>
> <br>
> Thanks in advance<br>
> <br>
> Best,<br>
> Kiran<br>
> <br>
> On Tue, Nov 3, 2020, 18:22 Lorenzo Paulatto <<a href="mailto:paulatz@gmail.com" rel="noreferrer noreferrer noreferrer" target="_blank">paulatz@gmail.com</a> <br>
> <mailto:<a href="mailto:paulatz@gmail.com" rel="noreferrer noreferrer noreferrer" target="_blank">paulatz@gmail.com</a>>> wrote:<br>
> <br>
> > Is there any methodology to check and decide nq-grid points for<br>
> phonon<br>
> > dispersion spectra calculations?<br>
> <br>
> I'm not sure what calculation you are trying to do.<br>
> Can you provide a more detailed description?<br>
> <br>
> Do not forget the second law of question-answer conservation:<br>
> «In a not-being-paid-for frame of reference,<br>
> the amount of time spent answering a question<br>
> will never exceed the amount of time spent asking it»<br>
> <br>
> <br>
> <br>
> -- <br>
> Lorenzo Paulatto - Paris<br>
> _______________________________________________<br>
> Quantum ESPRESSO is supported by MaX (<a href="http://www.max-centre.eu" rel="noreferrer noreferrer noreferrer noreferrer" target="_blank">www.max-centre.eu</a><br>
> <<a href="http://www.max-centre.eu" rel="noreferrer noreferrer noreferrer noreferrer" target="_blank">http://www.max-centre.eu</a>>)<br>
> users mailing list <a href="mailto:users@lists.quantum-espresso.org" rel="noreferrer noreferrer noreferrer" target="_blank">users@lists.quantum-espresso.org</a><br>
> <mailto:<a href="mailto:users@lists.quantum-espresso.org" rel="noreferrer noreferrer noreferrer" target="_blank">users@lists.quantum-espresso.org</a>><br>
> <a href="https://lists.quantum-espresso.org/mailman/listinfo/users" rel="noreferrer noreferrer noreferrer noreferrer" target="_blank">https://lists.quantum-espresso.org/mailman/listinfo/users</a><br>
> <br>
> <br>
> _______________________________________________<br>
> Quantum ESPRESSO is supported by MaX (<a href="http://www.max-centre.eu" rel="noreferrer noreferrer noreferrer noreferrer" target="_blank">www.max-centre.eu</a>)<br>
> users mailing list <a href="mailto:users@lists.quantum-espresso.org" rel="noreferrer noreferrer noreferrer" target="_blank">users@lists.quantum-espresso.org</a><br>
> <a href="https://lists.quantum-espresso.org/mailman/listinfo/users" rel="noreferrer noreferrer noreferrer noreferrer" target="_blank">https://lists.quantum-espresso.org/mailman/listinfo/users</a><br>
> <br>
<br>
-- <br>
Lorenzo Paulatto - Paris<br>
_______________________________________________<br>
Quantum ESPRESSO is supported by MaX (<a href="http://www.max-centre.eu" rel="noreferrer noreferrer noreferrer noreferrer" target="_blank">www.max-centre.eu</a>)<br>
users mailing list <a href="mailto:users@lists.quantum-espresso.org" rel="noreferrer noreferrer noreferrer" target="_blank">users@lists.quantum-espresso.org</a><br>
<a href="https://lists.quantum-espresso.org/mailman/listinfo/users" rel="noreferrer noreferrer noreferrer noreferrer" target="_blank">https://lists.quantum-espresso.org/mailman/listinfo/users</a></blockquote></div>