Dear Prof. P Blaha Thank you very much for yous fruitful suggestions. However, I did not change RKmax. For cubic Na only W_p_xx is enough but after making supercell (1 1 6) still I need only w_p_xx and forget about w_p_zz, though the system is tetragonal now. Is it right I understood? Second thing is it principally right that one converges SCF with small k-mesh say 30*30*5 and then use the same scf ao get OPTICAL properties with k-mesh say 90*90*15? I mean no need to converge scf with 90*90*15. Kind Regards
On Thu, Oct 29, 2015 at 9:03 PM, Peter Blaha <pbl...@theochem.tuwien.ac.at> wrote: > In principle you are doing thinks now correct. > In reality, however, we use the tetrahedra-method in the integration of > the BZ to calculate a joint-density-of-states. And for a metal !!! here > there is a difference between k-meshes in the small or large cell. (it is > related to the "back-folding" problem and in the supercell there are less > tetrahedra and thus less possibilities to interpolate for the tetrahedron > method than in the small cell). > > In any case, you need to consider two things: > > a) You have to decide to which accurcy a certain number should be > calculated. Typically, a plasma frequency would be quoted with one or two > digits after the comma (i.e. 5.9 or at most 5.94 eV). > > b) Then you have to converge the numbers with respect to k-mesh (but also > Rkmax !!) > Definitely you should use a ratio of 6:1 for the supercell, but eventually > you need to increase the mesh until there are no changes within the desired > accuracy. In your case, 90x15 is almost sufficient, but not quite if you > want two digits accuracy. > > c) in a cubic system, of course it is useless to quote two tensor > components and one is sufficient. > > > > > Am 29.10.2015 um 10:35 schrieb Muhammad Sajjad: > > Dear Prof. Blaha > > I did some calculation for Bulk Na (bcc, space gp #229_Im-3m) wiht k-mesh > 30*30*30 and found the plasma frequency (in case.outputjoint) as > Plasma frequencies: > > w_p_xx w_p_zz [eV] > > 5.9446 5.9446 > > Now I constructed a supercell 1*1*6 (definitely symmetry reduced and now > sp.gp is 1_P1), used k-mesh 30*30*5 and found > Plasma frequencies (much deviating from bulk values): > > w_p_xx w_p_zz [eV] > > 5.76146 5.3446 > > Then used k-mesh 90*90*15 and found > Plasma frequencies (w_p_zz is deviating from bulk w_p_zz ): > > w_p_xx w_p_zz [eV] > > 5.9485 5.8903 > > I have read the previous post ( > https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg09782.html) > but it is not speaking about w_p_zz. So when I plot epsilon data for > w_p_xx then it is matching with that of bulk but when I use w_p_zz then it > is definitely away from bulk. Should I consider w_p_zz or use "number > of choice = 1 in case.inop" and plot epsilon only with w_p_xx ? > > > Kind Regards > Muhammad Sajjad > Post Doctoral Fellow > KAUST, KSA. > > > _______________________________________________ > Wien mailing > listw...@zeus.theochem.tuwien.ac.athttp://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > SEARCH the MAILING-LIST at: > http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html > > > > _______________________________________________ > Wien mailing list > Wien@zeus.theochem.tuwien.ac.at > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > SEARCH the MAILING-LIST at: > http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html > > -- Kind Regards Muhammad Sajjad Post Doctoral Fellow KAUST, KSA.
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