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Dear Tayebeh,<br>
<br>
This difference between the "DOS" gap and the "band structure" gap is
simply related to the nature of the bands which define your gap.
Indeed, these bands are significantly dispersed (which means few states
at the top of the valence band and at the bottom of the conduction
band). As a consequence, it leads to a slow increase of the DOS (few
states) and the DOS starts to be significant only at higher energy
values, which means that the apparent gap is larger than the
fundamental gap obtained from the band structure. <br>
Similar question arise when asking the difference between fundamental
gap and optical gap. In the optical gap the notion of efficiency enter
in terms of transition probability but also in terms of number of
states, if the band structure is strongly dispersed and also if the
transition is allowed, the optical gap will be larger than the
fundamental gap. <br>
<br>
Hope that this will help you<br>
<br>
Regards<br>
<br>
Xavier<br>
<br>
<br>
taiiebeh molarooy a écrit :
<blockquote cite="mid560753.22043.qm@web33604.mail.mud.yahoo.com"
type="cite">
<div class="MsoNormal"
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style="font-size: 10pt; color: rgb(51, 51, 51); font-family: Arial;">Dear
wien users,</span></div>
<div class="MsoNormal"
style="margin: 0cm 0cm 0pt; direction: ltr; line-height: 14.4pt; unicode-bidi: embed; text-align: left;"><span
style="font-size: 10pt; color: rgb(51, 51, 51); font-family: Arial;">Hi,
I have calculated electronic structure of CNT, but there is any problem
with value of band gap.<o:p></o:p></span></div>
<div class="MsoNormal"
style="margin: 0cm 0cm 0pt; direction: ltr; line-height: 14.4pt; unicode-bidi: embed; text-align: left;"><span
style="font-size: 10pt; color: rgb(51, 51, 51); font-family: Arial;">The
value of band gap from band structure is less than DOS. For example bad
gap of CNT(10-0) from band structure is calculated about 0.35 eV while
it is 0.9 eV from DOS. And also for CNT(16-0) with 64 atom, it is about
0.5 eV while it is 1.2 eV from DOS. <o:p></o:p></span></div>
<div class="MsoNormal"
style="margin: 0cm 0cm 0pt; direction: ltr; line-height: 14.4pt; unicode-bidi: embed; text-align: left;"><span
style="font-size: 10pt; color: rgb(51, 51, 51); font-family: Arial;">Do
you know why the value of band gap is different?<o:p></o:p></span></div>
<div class="MsoNormal"
style="margin: 0cm 0cm 0pt; direction: ltr; line-height: 14.4pt; unicode-bidi: embed; text-align: left;"><span
style="font-size: 10pt; color: rgb(51, 51, 51); font-family: Arial;"> <o:p></o:p></span></div>
<div class="MsoNormal"
style="margin: 0cm 0cm 0pt; direction: ltr; line-height: 14.4pt; unicode-bidi: embed; text-align: left;"><span
style="font-size: 10pt; color: rgb(51, 51, 51); font-family: Arial;">Another
problem is that we are expected that value of band gap must be
decreased by increasing diameter of CNT, while my results is inverse!<o:p></o:p></span></div>
<div class="MsoNormal"
style="margin: 0cm 0cm 0pt; direction: ltr; line-height: 14.4pt; unicode-bidi: embed; text-align: left;"><span
style="font-size: 10pt; color: rgb(51, 51, 51); font-family: Arial;">Do
you know why are these problems?<o:p></o:p></span></div>
<div class="MsoNormal"
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style="font-size: 10pt; color: rgb(51, 51, 51); font-family: Arial;"> <o:p></o:p></span></div>
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style="font-size: 10pt; color: rgb(51, 51, 51); font-family: Arial;">Thank
you very much in advance.<o:p></o:p></span></div>
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style="font-size: 10pt; color: rgb(51, 51, 51); font-family: Arial;">Yours
sincerely,<o:p></o:p></span></div>
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style="font-size: 10pt; color: rgb(51, 51, 51); font-family: Arial;">Tayebeh.<o:p></o:p></span></div>
<p> </p>
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