[Wien] How to calculate optical absorption edge ?
Masood Yousaf
masoodyousaf1 at yahoo.com
Tue Jul 9 12:11:50 CEST 2013
Sir sorry for inconvenience again. I found small small software utility TANGENT.opk for ORIGIN which can draw tangent a point and gives corresponding slope. I am just confused at which point I should take the tangent. What point in data set of imaginary part of epsilon represents ''EDGE''. In other words which point represent ''EDGE''. Kindly guide how to take tangent properly in Origin along Edge.
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 2:52 PM
>Subject: Re: [Wien] How to calculate optical absorption edge ?
>
>
>
>I am also using origin to determine the absorption edge based on epsilon2.
>You must simply draw a tangent line along the edge and then read
the intersection between this line and "Eps2 = 0" axis.
>
>
>
>
>Le 7/9/2013 8:44 AM, Masood Yousaf a écrit :
>
>I would be grateful if you guide me how to apply this tangent method to the data of imaginary part of the dielectric function. can I use Origin to apply this ?
>>
>>
>>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 2:30 PM
>>>Subject: Re: [Wien] How to calculate optical absorption edge ?
>>>
>>>
>>>
>>>If you plot epsilon2 (the imaginary part of the dielectric function) and use the tangent method, you can estimate the absorption edge from WIEN2K.
>>>However, it requires to use a proper functional,
allowing to overcome the inherent problems of
DFT, which is a ground state theory, i.e. LDA+U
for correlated systems or hybrid functional...
>>>
>>>Regards
>>>
>>>Xavier
>>>
>>>Le 7/9/2013 7:00 AM, Masood Yousaf a écrit :
>>>
>>>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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>>>>
>>>>
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