[Wien] optic sum rules

[Rocquefelte]

There is definitely no need to go to such a high number of k-points.
In the paper of Claudia, they were looking at metallic compounds, for 
which we need to have a very dense k-mesh (for the intraband transitions).
In your case you expect a semiconductor and thus you will have only 
interband transitions. Thus 6000 kpoints is already converged to my 
point of view.
I should say that the best way to insure the convergency in the present 
case is to plot the epsilon2 as a function of the energy for instance 
and to compare this quantity with different k-meshes. In your case, try 
to do 300 kpoints first and then 500, 1000, 2000, 3000 kpoints ... You 
will certainly reach the convergency at about 1000-2000 kpoints ...

Regards

Xavier
P.S.: The values obtained for 90000 kpoints are curious but I imagine 
that you had a prob


Le 9/30/2013 4:59 PM, ali ghafari a écrit :
> Dear Prof. Blaha
>
> I have calculated the optical properties of TiSe2 by MBJ potential 
> with 6000, 50000 and 90000 kpoints which generated after scf by x kgen 
> as discussed in the UG.
> As discussed in the paper of Prof. Claudia Draxl (computer physics 
> comm. 175, 1-14 (2006)) the sum rule 1 and 2 show 'an effective number 
> of electrons contributing to the absoption process as a function of 
> energy'.
> but my calculations lead to :
> 6000 kpoints:
> sum rule 1: Int(sigma)dw      19.14
> sum rule 2: Int(eloss.w)dw    18.93
> sum rule 3: Int(eloss/w)dw    1.51
> 50000 kpoints
> sum rule 1: Int(sigma)dw      19.08
> sum rule 2: Int(eloss.w)dw    18.94
> sum rule 3: Int(eloss/w)dw    1.52
>   
> 90000 kpoints
>
> sum rule 1: Int(sigma)dw      10.125
> sum rule 2: Int(eloss.w)dw    10.035
> sum rule 3: Int(eloss/w)dw    1.51
> the results show that in 90000 kpoints the value of 'sum rule 2' 
> significantly decreases . in the UG it has mensioned that for the 
> optic we need dense kpoints but how many? how can I check it for optic?
> Best Regards
> Ali
>
>
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