[Wien] optic sum rules

[ali ghafari]

Dear Xavier

thank you very much for your reply. 
Actually, I have repeated the calculations again. I see the spectra are almost 
same for 2000 and 3000 kpoints but still there is a significant change in the spectra for 90000 kpoints.
how can I explain it? furthermore, when you said 2000, 3000 kpoints, your means is in the
 BZ or IBZ?
Best Regards
Ali




________________________________
 From: Rocquefelte <xavier.rocquefelte at cnrs-imn.fr>
To: A Mailing list for WIEN2k users <wien at zeus.theochem.tuwien.ac.at> 
Sent: Monday, September 30, 2013 6:43 PM
Subject: Re: [Wien] optic sum rules
 


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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