BandStructure - Extended Huckel Method

[Luis M. Villamagua C.]

Good day ATK user,

I have been following this tutorial:
http://www.quantumwise.com/documents/tutorials/ATK-11.8/BasicGrapheneTutorial/index.html/chap.armchairribbon.html

At the end, they recommended to redo the calculations for different types of ribbons (armchair/zigzag) and for different widths because band gap is strongly dependent on both factors!

I have been testing upon Na-AGNR (Na ranging from 4 to 13) and indeed the band gap varied as expected. I could even recongnize the 3m, 3m+1 and 3m-1 group.

When I try to analyze the same AGNRs but repeted 15 times in the z direction, I get something strange, or at least something that I do not understand. I get too many straight and almost parallel lines (see attached 1 and 2). Also the Ef is not at the center anymore. Can you help me understanding the physical meaning of this?

btw the bandStructure is calculated using Extended Huckel method; to what extent can I trust these results? If for example, I have distorted edges or vacancies,  can I still trust the results obtained?

The attachments represent the Band Structure for a 4AGNRx15.


Many many thanks,
Luis

[Anders Blom]

I'm fairly sure the effect you're seeing is simply a results of Brillouin zone folding.

The fact that the Fermi level is not symmetrically placed in the band gap is just a cosmetic issue without physical significance. However, we did improve this for 2014, and I think it will be always symmetric in the new version (not published yet).