Dear  Lyudmila and BHamu
Thank you for your suggestions. I have already used 18*18*3 for supercell
and 18*18*18, but found difference in plasma frequency for supercell and
bulk.  Should plasma frequency be same for bulk and supercell? or I should
use the new plasma frequency obtained from super cell calculation?

@Lyudmila
| In terms of accuracy, this is the worst.
but why?



On Tue, Oct 13, 2015 at 10:55 AM, Dr. K. C. Bhamu <kcbham...@gmail.com>
wrote:

>
>
> Dear sajjad
>
> I am also a beginner but I must suggest you to choose 18*18*3 k points for
> 1*1*6 supercell in comparison with bulk.
> As volume in real space is inversely proportional to volume of reciprocal
> space. Larger the volume in real space lower the volume in reciprocal
> space. So while computing properties of 1*1*6 structure you are minimizing
> your volume in z direction and hence need less k-points.
>
> I appreciate any comment on this from DFT experts.
>
>
> Sincerely
> Bhamu
>
> I have computed PF for bulk Na and its value is  *5.943 eV* with k-mesh
>> *18*18*18*.
>>
>> Then I constructed a supercell 1*1*6
>>
>
> ...>>>>>>> use 18*18*3 k points for 1*1*6 supercell.
>
> and run the calculation with different k-meshes and obtained PF values.
>> The details are
>>
>> *K-mesh                        PF (x/z components in eV)*
>>
>> *24*24*24                  5.7097   /   5.8192*
>>
>>
>> *36*36*24                  5.7614   /   5.8098  *
>>
>>
>> *50*50*10                  5.9358   /   5.6280 *
>>
>> *50*50*30                  5.9365   /   5.8079*
>>
>> My question is why PF is very sensitive to k-mesh selection? and which
>> value of PF is required for correct dielectric constant calculation? Do I
>> need *PF = 5.943 eV* for the supercell and then, definitely, need more
>> test calculation for right k-mesh selection?
>>
>> --
>> Kind Regards
>> Muhammad Sajjad
>> Post Doctoral Fellow
>> KAUST, KSA.
>>
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>
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-- 
Kind Regards
Muhammad Sajjad
Post Doctoral Fellow
KAUST, KSA.
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