The google lookup for GNR gives "gotta nigga rolling". Probably, he falls out at the edges. You might guess how the abbreviations annoy people. 

Dear sir

what i mean by GNR is graphene nano ribbon sir,yeah its true i should have given full fom of this one,now which i have done.Please give your reply,if u have any idea.

Thanks

I am far from this but you may ask Alexander Onipko or look at his papers 

ok thanks sir.

regards

If you are looking for edges in gnrfet, you can follow this paper.

http://scitation.aip.org/content/aip/journal/apl/91/7/10.1063/1.2769764

Thanks Brajesh ,can you please tell me how to add magnetic term in Hamiltonian ,if any idea,what work you have done on Mosfet based on graphene materials.

regards

To account magnetic field in the tight binding Hamiltonian matrix, you can follow this paper.

http://www.condmat.physics.manchester.ac.uk/pdf/mesoscopic/publications/graphene/RMP_2009.pdf