Hi thanks for the reply. I need to compute a sort of finite temperature electron-phonon coupling, so I needed to go into the code and I wrote my own routine to do that, I am debugging the code and I noticed that the result at different but equivalent q points, let's say X=(1,0,0) and X=(1,1,0) in FCC are not the same as I should expect. Then I noticed that the wave function (evq) in reciprocal space differs (that is expected) but I do not understand the relation between the two, that was why I was asking the previous question. In the meantime I found a mistake in the way I was computing the potential derivative, that is probably the main source of my problem. I was wondering also what does the routine symdyn_munu_new exactly do? Why does the dynamical matrix have to be symmetrized in the basis of the modes ?
Thanks in advance, Jacopo Simoni, Lawrence Berkeley National Lab. On Mon, 27 Sept 2021 at 00:20, Lorenzo Paulatto <paul...@gmail.com> wrote: > Hello Jacopo, > instead of answering your question, I may ask you what you actually want > to do, because chances are that your problem has already been met by others. > > E.g. there are ways to eliminate this phase, or to neutralize it to > compute the derivative w.r.t. the wave vector. But more often, when you > have an observable quantity that comes from a sum over the k-points, the > phases will cancel out in the total, if done correctly. It is actually a > good way to check that your formulas are correct. > > Hth > > -- > Lorenzo Paulatto > > On Sat, Sep 25, 2021, 21:28 Jacopo Simoni via users < > users@lists.quantum-espresso.org> wrote: > >> So this means the phase factor is of the form e^{iG(k)r} where G(k) is >> the translation vector in rec. space such that >> G(k)+q+k=q'+k' (inside the first Brillouin zone) >> the phase factor is therefore dependent on the k vector and in reciprocal >> space the wave functions of the two equivalent q points are shifted by the >> vector G(k) ? >> Is there a variable in the code corresponding to this vector G or to the >> phase factor itself ? >> >> >> On Sat, 25 Sept 2021 at 03:42, Paolo Giannozzi <p.gianno...@gmail.com> >> wrote: >> >>> On Sat, Sep 25, 2021 at 2:00 AM Jacopo Simoni via users < >>> users@lists.quantum-espresso.org> wrote: >>> >>> This wave function appears different from the wave function at an >>>> equivalent q point, for instance if I look at evq at q=(0,0,1), this is >>>> different from evq at (1,1,0) that are equivalent by translation of a G >>>> vector (I am thinking here at a FCC periodic lattice). The two functions >>>> just differ by a phase factor or I am missing something ? >>>> >>> >>> They differ by a phase factor; moreover, in the presence of degenerate >>> eigenvalues, you have no guarantee that the eigenvectors in the degenerate >>> subspace are the same. Finally, the ordering of k+G components is not >>> necessarily the same in the two cases >>> >>> Paolo >>> >>> Thanks in advance, >>>> Jacopo Simoni, Lawrence Berkeley National Lab. >>>> _______________________________________________ >>>> Quantum ESPRESSO is supported by MaX (www.max-centre.eu) >>>> users mailing list users@lists.quantum-espresso.org >>>> https://lists.quantum-espresso.org/mailman/listinfo/users >>> >>> >>> >>> -- >>> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche, >>> Univ. Udine, via delle Scienze 206, 33100 Udine, Italy >>> Phone +39-0432-558216, fax +39-0432-558222 >>> >>> _______________________________________________ >> Quantum ESPRESSO is supported by MaX (www.max-centre.eu) >> users mailing list users@lists.quantum-espresso.org >> https://lists.quantum-espresso.org/mailman/listinfo/users > >
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