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. BlahaI did some calculation for Bulk Na (bcc, space gp #229_Im-3m) wihtk-mesh 30*30*30 and found the plasma frequency (in case.outputjoint) asPlasma frequencies: w_p_xx w_p_zz [eV] 5.9446 5.9446Now I constructed a supercell 1*1*6 (definitely symmetry reduced andnow sp.gp <http://sp.gp> is 1_P1), used k-mesh 30*30*5 and foundPlasma 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 5.8903I 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 forw_p_xx then it is matching with that of bulk but when I use w_p_zzthen it is definitely away from bulk. Should I consider w_p_zz oruse "number of choice = 1 in case.inop" and plot epsilon only withw_p_xx ?Kind Regards Muhammad Sajjad Post Doctoral Fellow KAUST, KSA. _______________________________________________ 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

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