[Wien] How to calculate optical absorption edge ?

[Masood Yousaf]

Dear Sir, thanks for your elaboration. Need some further explanation to overcome the confusion. Is it possible to determine accurately absorption edge from WIEN2k code only i.e., from case.epsilon ?  


Best wishes
Masood



>________________________________
> From: Rocquefelte <xavier.rocquefelte at cnrs-imn.fr>
>To: A Mailing list for WIEN2k users <wien at zeus.theochem.tuwien.ac.at> 
>Sent: Tuesday, July 9, 2013 12:40 PM
>Subject: Re: [Wien] How to calculate optical absorption edge ?
> 
>
>
>Experimentally an absorption edge (optical gap) is estimated using the tangent method. 
>Thus you should do the same with your calculated data to compare
      optical gap values, which differ from a fundamental band gap. 
>
>Indeed, a fundamental band gap is the smallest band gap allowing
      to excite an electron in unoccupied states (deduced from
      electrical measurements - thus no transition rules). 
>In contrast, the optical gap is related to an excitation using
      photons, thus it respects the dipolar transitions rules (this gap
      is usually larger than the fundamental band gap). 
>
>Regards
>
>Xavier
> 
>
>Le 7/9/2013 3:07 AM, Masood Yousaf a écrit :
>
>Dear wien2k users
>>
>>Kindly suggest how to calculate optical absortion edge in wien2k
        ? How it differs from band gap of material ? I read that first
        critical point in imaginary part of the dielectric function
        represents optical absorption edge. But how to ensure that which
        is the first critical point. Kindly guide
>>
>>
>>Best wishes
>>Masood
>>Universiti Tecknologi Malaysia
>>
>>
>>
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