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