Dear Dario, For calculation of dielectric properties you need to do integrations over the BZ. For high symmetry lattices, a shifted k-point mesh (specially a k-pt mesh without Gamma pt.) without the high symmetry points should be used. In that way you have a better sampling of your BZ and hence a improvement in the results. I also found similar improvements of convergence when I tested for convergence of adsorption energy wrt k-point mesh.
Prasenjit. 2008/10/10 dario rocca <roccad at gmail.com> > > Dear Users > I have an issue related to the convergence of the static dielectric matrix > using the PH code. I have performed calculations > on bulk silicon using different k point meshes and I have obtained the > following results: > > k grid diagonal component of number of k points in > the dielectric tensor the irreducible > Brillouin zone > > 4*4*4 23.668350065 8 > 6 *6*6 16.297485614 16 > 8 *8*8 14.044830694 29 > 10 *10*10 13.288531964 47 > 12*12*12 13.029602882 72 > 16 *16*16 12.908820645 145 > 20 *20*20 12.894538380 256 > > k grid+ 1 1 1 shift diagonal component of number of k > points in > the dielectric tensor > the irreducible Brillouin zone > > 4*4*4 13.840844632 > 10 > 6*6*6 > 12.997009732 28 > 8*8*8 > 12.903849607 60 > 10*10*10 12.893711596 > 110 > 12*12*12 12.892685597 > 182 > 16*16*16 12.892482798 > 408 > 20*20*20 12.892537346 > 770 > > I was surprised of the improvement in the convergence due to the shift of > the grid. I don't think this is related to the number of k points > in the IBZ (at least not exclusively). > I have observed a similar behavior in diamond. > The ground state energy convergence also benefits from the shift, but the > improvement is not so striking. > Does someone has any hint on why the shift of the grid improves the > calculation of the dielectric properties of silicon? > Thanks a lot > Dario Rocca, dept. of chemistry, UC Davis > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > > -- PRASENJIT GHOSH, POST-DOC, ROOM NO: 265, MAIN BUILDING, CM SECTION, ICTP, STRADA COSTERIA 11, TRIESTE, 34104, ITALY PHONE: +39 040 2240 369 (O) +39 3807528672 (M) -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20081010/e4d3a952/attachment.htm