Armchair graphene nanoribbon (band structure and transmission spectrum)

[bfazi]

Hi all
I calculated the band structure and transmission spectrum of an armchair graphene nanoribbon (AGNR) without passivization with two different methods:
1-DFT with PBE exchange correlation
2-ATK-SE: Extended Huckel with Cedra.carbon [graphite] basis set
For both of them I used 1*1*100 k-point sampling
But the results are quite different!!!
The DFT result showed the AGNR is metal but The Extended Huckel result showed the AGNR is semiconductor! (I attached the results and AGNR structure)
Can anyone help me please?

[Anders Blom]

Add passivation in DFT. The results without passivation are wrong.

[Anders Blom]

Prof. Anders Blom
If I want to use the AGNR without passivation

Why is this important for you? Passivation is a numerical trick to remove unphysical surface states in the band gap. Non-selfconsistent Huckel doesn't need this (because there is no charge transfer) but then you also cannot really consider finite bias or anything interesting - for that you need selfconsistency and then you need passivation also in Huckel, just like we show in many tutorials on GNRs.

[Anders Blom]

Probably yes. If you want help to decide what, it might make sense to tell us how you did the calculation...

[Anders Blom]

Aha, I just noticed that the passivating H atoms are only added to the N atoms, when you build it via the Nanoribbon plugin. That seems like a bug...

Try removing the H atoms and then add them using Coordinate tools>Custom passivator instead (sp2). Then, optimize the structure, and calculate the band structure. Even without optimization, however, you will get a band gap of about 4.8 eV.

[Anders Blom]

The hydrogen passivation is not added for fun - it serves a clear purpose, to saturate the dangling bonds on the  surface. If this is not done, unphysical surface states will appear and result in an incorrect electronic structure.