Dear Paolo, Thanks for your reply.I do choose q points using Monkhorst-Pack K mesh. But I am still upset. I already increased the K mesh to 48 48 48 when I calculated the EP coupling. To test the performance in several high symmetry q points, I still got the results for phonon linewidth far away from the experimental data, despite I obtained the good results for phonon. :-(
Any comments? Best Wishes! Yanming Ma > > I have been puzzled by the calculation of the electron-phonon (EP) > > coupling coefficient lambda using PWSCF > >me too... > >The calculation of the electron-phonon coupling coefficients >is presently done using a simple but not-so-smart algorithm: >for each phonon q one calculates \lambda(q), performing a >(slowly convergent) sum over k of electronic states. > > > My question is how to choose the q points properly in the first BZ? > >choose a uniform grid (Monkhorst-Pack, for instance) and pick q-points >in the irreducible BZ. Unless your \lambda(q) is strongly anisotropic >(this is the case of MgB_2, for instance: most of the contribution to >\lambda comes from a specific phonon branch), the convergence wrt >the q-grid shouldn't be a big problem. > > > So My question is what is the criterion for the EP coupling convergency. > >it is more or less the same criterion that is used to check for >convergence in metals: you should try increasingly dense k-point >grids and a range of gaussian broadenings for each grid. You should >find a range of gaussian broadening and of k-point grids for which >the value of \lambda(q) is reasonably constant. Unfortunately this >usually happens with rather large grids. > >There is some ongoing work on a better algorithm for calculating >electron-phonon coupling coefficients using tetrahedra. > >Paolo >-- >Paolo Giannozzi e-mail: giannozz at nest.sns.it >Scuola Normale Superiore Phone: +39/050509412 >Piazza dei Cavalieri 7 Fax: +39/050509417, 050563513 >I-56126 Pisa, Italy Office: Lab. NEST, Via della Faggiola 19 > >_______________________________________________ >Pw_forum mailing list >Pw_forum at pwscf.org >http://www.democritos.it/mailman/listinfo/pw_forum _________________________________________________________________ ??????????????? MSN Hotmail? http://www.hotmail.com
