Hi Gosia > No, it is not not correct. Look to the definition of el-ph > in one of Savrasov's papers and you will see that that there is > double delta on Fermi surface. You can split the integration over > phonon vectors (q-points) and over electron momentum (k-points) > if you first integrate over phonons and later over electrons. > Not the other way around. Just because there is delta_k+q delta_k .
the el-ph coefficients in PWscf are presently calculated by performing the sum over k at a given q, then summing the results over q. Maybe I haven't understood your point: are you implying that this is not correct? While I agree that the present implementation is dumb and ineffective, I don't see anything wrong with it. > You try to integrate delta_k * delta_q or delta_k+q * delta_q > if I understand correctly your e-mail. > If you start from the integration over k first then at q=0 you meet > the problem of delta_k*delta_k+0 which is mathematically not defined. A gaussian broadening scheme is used to deal with the double delta. In this scheme, the double delta should be defined also for q=0. Maybe what bothers you is that in the q=0 limit the function to be summed contains a 1/\omega^2 term. I "solved" the problem by averaging over translated grids (that do not include q=0). For an estimate of \lambda - that is what most people want - this should be good enough. For an accurate value of \lambda, I don't know, but getting an accurate value of \lambda is difficult anyway 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
