Howto calculate the band structure of graphene numerically from the graph?

[nanomanisha]

I am using ATK 11.2.2 and calculating the band structure of graphene. I just want to know the procedure of numerically calculating the value of band gap in graphene??

[zh]

It is well known that gaphene is a zero-gap material.

[nanomanisha]

I agree with you. But I am asking about armchair garphene nanoribbon that shows some band gap. In addition to this, functionalized GNR also shows some band gap. So in that case how can we calculate the band gap numerically?
Second I also want to know what does the density of states interpret in case of graphene??

[zh]

In the band structure of graphene structure, if there is a gap around the Fermi level, you can pick up the energy for the bottom of conduction band and also the one for the top of valence band. These two values are used to estimate the band gap.