On Wednesday 19 March 2003 16:43, ma Yanming wrote: > 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
