[Wien] How to calculate optical absorption edge ?

[Rocquefelte]

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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