Determining Bandgap

[Dipankar Saha]

Dr. Nordland,
first thing first......thanks a lot for all the details....   /

Next, as the recipe provided by you.... I did it with the 8-AGNR unit cell.../ I have included the *.py files for both, defect and without defect.....In one case NR is S.C. ...in other it seems to be metallic. Now, how can I find that,
1 ) Whether, a surface state or defect state that has been introduced in the band gap or not??
2)The quantum no. value ...for materials having more than one different atoms in there unit cell??

3) Besides, as per the Band Struct. for metallic.... Are you meaning the k-point 0.65... exactly where the crossing of the bands happened??

[Nordland]

Okay - I looked a little at your system and I would like to raise a few remark. First of all the semi-conducting system has a band gap of 0.01 eV - This means that this is metallic in any real world case, since any finite temperature would make it possible to lead current quite well.

Secondly the defect on which you impose on your system is major effect on the system. Let me try to do the same calculation on a different system so you can see what kind of analysis I would have done.

[Nordland]

Please see my attached calculation - they gives a mucher better view of how a defect effect the bandstructure of a ribbon.

[Dipankar Saha]

Sir, in all the three cases.....BG vlues are somewhere around 0.6 eV ... 0.58,0.64,0.64 eV....those are pretty much fair..(considering the case of any AGNR)!!! /
But, in perfect one Bloch sates are residing at the edges...almost diagonally apart; in case where the defect is in the center...those are well distributed over the entire system; and for the edge defected one...all of those can be found near to a particular edge only..... /
1) Now, what is the inference that can be drawn from all these??
2) What it (Bloch States) would have been...if, in one of the cases,  it behaved as metallic??

[Dipankar Saha]

Dr. Nordland

Sir, it will be very helpful...to conclude the entire discussion on this topic...with a more clear view..., if you kindly share your view points regarding those results, that I have stated in my earlier post...........

[Dipankar Saha]

Sir
Please find the attachments... which are showing the Bloch states distribution of the 'perfect_ribbon' and 'Center_defect_ribbon'........ all are taken at the G-point........

[Arya]

Hi,

Not sure if my question fits under current discussion. But can anyone help me to understand how the right part of figure 6.30 is obtained from the left of figure 6.30 in following link

http://www.eng.fsu.edu/~dommelen/quantum/style_a/emc.html#SECTION075225000000000000000


Thanks in advance!
-Arya

[ramkrishna]

Hi Arya,
    I feel, the easiest way is, extract the band structure and DOS data and plot side by side in any plotting tools. Then you can visualize the same type of figure like 6.30 in that link.

Ramkrishna

[Arya]

Hi Ramkrishna,

Thanks for reply. Of course I can do what you suggested. However, I wanted to get the intuition on how DOS is plotted by looking at Bandstructure; (as in the given link) . This is just to understand DOS and other theories better.

-Arya

[ramkrishna]

Here, DOS is the total density of state form different subbands of the crystal. So, it is not an easy way to get the intuition of DOS just form the bandstructure itself when it is a real crystal (not a free electron gas).  Even that link also describes this thing. The figure 6.30 describes only which part of the band contributes more in the total DOS.
If you are looking for the DOS in a subband then you can check the following link. It may help you.
http://quantumwise.com/forum/index.php?topic=2275.0#.UpO0UsSshcY

[Arya]

I do understand than DOS is not intuitive for complex bandstructure. To be more specific if I have a bandstructure what decides the height of histogram in figure 6.30 (on the link above). Is it the value of K in small energy range on vertical axis for all subbands?

[Dipankar Saha]

Sir,
It will be very helpful...to conclude the entire discussion on this topic...with a more clear view..., if you kindly share your view points regarding those results, that I have stated in my earlier post...........

That was~~~
[[ ................................     In all the three cases.....     BG vlues are somewhere around 0.6 eV ... 0.58,0.64,0.64 eV....those are pretty much fair..(considering the case of any AGNR)!!! / But, in perfect one Bloch sates are residing at the edges...almost diagonally apart; in case where the defect is in the center...those are well distributed over the entire system; and for the edge defected one...all of those can be found near to a particular edge only..... /
1) Now, what is the inference that can be drawn from all these??
2) What it (Bloch States) would have been...if, in one of the cases,  it behaved as metallic?? ................................. ]]