question about bandstructure

[esp]

I am not sure if I can explain this well but i will try ..

I did some calculations of bandstructure for graphene ribbons .. now to do this i understood that i needed a sort of unit cell, which for GNRs, is a sort of GNR with a very short length, like 2 hex rings long ... now, i wanted to see the change when doped, so i doped the graphene and i can see the bands shift up and down, n type, p type, etc ... now suppose i want to see the effect of variation ... so the idea is, you dope the graphene, but doping with dopant atoms (although not even possible today), assume it is possible at some time, and there is some variation in the position of the atoms ... Now, if  i want to see the bandstructure change not for a short 2 ring section, but for an entire electrode that is longer, then it all flattens out so that there is no more linear dispersion, etc .. so how can i get to what i am looking for, using atk, in a simple way?  

What i want to know is, for example, if doped and no variation gives Ev, Ec, and Ef values of e1, e2, e3, with some variation, how do these energy levels change? This is easy when the length is short, because for example the band edges are still discernable  .. but when it is longer it is hard to tell

Does this make sense?  if not i can try with pictures

[Anders Blom]

A picture would help, but also perhaps a clearer concept of what physics you are looking for. The bandstructure can "change" in many ways, due to various things, but is the primary effect change in effective mass, or band gap, or just the Fermi level position as a result of the doping. And - ultimately - why is the change in band structure relevant, for what physical observable?