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<div class="moz-cite-prefix">If you plot epsilon2 (the imaginary
part of the dielectric function) and use the tangent method, you
can estimate the absorption edge from WIEN2K.<br>
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...<br>
<br>
Regards<br>
<br>
Xavier<br>
<br>
Le 7/9/2013 7:00 AM, Masood Yousaf a écrit :<br>
</div>
<blockquote
cite="mid:1373346047.8274.YahooMailNeo@web121105.mail.ne1.yahoo.com"
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<div style="color:#000; background-color:#fff; font-family:times
new roman, new york, times, serif;font-size:12pt">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 ?
<br>
<div><br>
</div>
<div>Best wishes<br>
Masood<br>
<br>
<blockquote style="border-left: 2px solid rgb(16, 16, 255);
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<div style="font-family: times new roman, new york, times,
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<div dir="ltr">
<hr size="1"> <font face="Arial" size="2"> <b><span
style="font-weight:bold;">From:</span></b>
Rocquefelte <a class="moz-txt-link-rfc2396E" href="mailto:xavier.rocquefelte@cnrs-imn.fr"><xavier.rocquefelte@cnrs-imn.fr></a><br>
<b><span style="font-weight: bold;">To:</span></b> A
Mailing list for WIEN2k users
<a class="moz-txt-link-rfc2396E" href="mailto:wien@zeus.theochem.tuwien.ac.at"><wien@zeus.theochem.tuwien.ac.at></a> <br>
<b><span style="font-weight: bold;">Sent:</span></b>
Tuesday, July 9, 2013 12:40 PM<br>
<b><span style="font-weight: bold;">Subject:</span></b>
Re: [Wien] How to calculate optical absorption edge
?<br>
</font> </div>
<div class="y_msg_container"><br>
<div id="yiv2164697746">
<div>
<div class="yiv2164697746moz-cite-prefix">Experimentally
an absorption edge (optical gap) is estimated
using the tangent method. <br>
Thus you should do the same with your calculated
data to compare optical gap values, which differ
from a fundamental band gap. <br>
<br>
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). <br>
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). <br>
<br>
Regards<br>
<br>
Xavier<br>
<br>
<br>
Le 7/9/2013 3:07 AM, Masood Yousaf a écrit :<br>
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<div
style="color:#000;background-color:#fff;font-family:times
new roman, new york, times,
serif;font-size:12pt;">Dear wien2k users<br>
<br>
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<br>
<br>
<div>Best wishes<br>
Masood<br>
Universiti Tecknologi Malaysia<br>
</div>
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<br>
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