Dear Professor Blah
Thank you for your quick response.  Yes I found that completely converged
(with the best k-mesh) leads to the same results on changing k-meshes for
optical properties. Na is better in k-mesh selection than that of Al.

Actually I am expanding  structure in z-direction. In my opinion, I must
consider both w_p_xx and w_p_zz, as former is changing slowly while an
abrupt change is found in the later component of PF. Am I right?
Simply, except cubic system, both tensor components of PF must take in
account?
True Regards

On Fri, Oct 30, 2015 at 9:28 AM, Peter Blaha <pbl...@theochem.tuwien.ac.at>
wrote:

> Usually, different properties require different k-meshes. So it should be
> ok to converge the scf with a smaller k-mesh (it still must be a "good"
> one), but use more k-points for a plot of the DOS or optics.
>
> Please repeat the optics calculation with a series of k-meshes and plot
> w_p as funktion of the k-mesh. You should find out in this way the
> converged value.
>
> PS: I know that for Al one needs MANY more k-points to get a converged
> value. No idea about Na.
>
>
> Am 29.10.2015 um 21:50 schrieb Muhammad Sajjad:
>
> 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>
>> 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.
>>
>>
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>
>
> --
> Kind Regards
> Muhammad Sajjad
> Post Doctoral Fellow
> KAUST, KSA.
>
>
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-- 
Kind Regards
Muhammad Sajjad
Post Doctoral Fellow
KAUST, KSA.
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