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 <http://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.
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