Hi Surender,

Based on your topics description, I guess that you are professional on grapheme. For my view, GO is bandgap is  ~ 0 eV. I choose Kubleka-Munk method to evaluate the bandgap of semiconductor. I do not use this to evaluate the bandgap of GO. Thanks.

Thanks Zhong,not exactly but i am learning also,earlier we have taken our system as silicon wire in 1-dimension but now we have done with CNT,just after rolling a graphene sheet with chirality keeping in mind,ie m,n having diameter app 1nm,in case SWNT(single walled nanotube),now i am working hard with GNR.

regards

Thanks,Chuong Nguyen for your nice advise.I was doing it with NEGF where i dont need pseudopotentials actually ,i was trying it with Quantum Transport equation with Poisson equation .I am getting Hamiltonian ,since i have made it 1-D problem now since at same time there will be two hoppings at same time and we cant solve it easily.BTW Thanks a lot.I'll see your paper.

regards

best wishes

Hello Tiwari G,thanks for your concern,i want to solve it with NEGF approach so please let me know if you any idea about this.since i dont know about DFT,although DFT works at equilibrium situation while i have non equilibrium situation,so hope you understnad my doubt.

regards

DFT is a method to find the ground state of a system. Therefore you must not expect to find the correct value of the gap in semiconducting systems. For a more accurate value of the gap you need to use beyond-DFT methods, like for instance GW or TD-DFT.

Ok thanks Fthenakis ,dear sir i want to use DFT for my Graphene nano ribbon ,is it possible sir for my system?

regards

Sure you can use DFT for graphene nanoribbons. Of course you can not expect that the band gaps will be reliable, but in principle it is expected that the trend (i.e. the comparison with each other gap) will be correct.

Thanks but sir ,here in case of Graphene nano ribbons gap will depend upon the width directionm,while such things were not in case of CNT(Carbon nano tube).If i wants to use DFT sir ,what will be the required things for that since in my matlab code i have written ,i am getting only EK relation ,conductance and LDOS sir.

regards

Dear Surender,

I m not sure I have understood what you are asking. It i expected that if a gap exists, it would depend on the width of the ribbon and its chirality. This is what you will find if you use a simpe hueckel model (i.e. a hamiltonian with first neighbour interactions of only p_z orbitals directed perpendicular to the ribbon surface). For a more accurate (DFT) calculation you will need to optimize tha graphene ribbon structure first. I hope I have answered your question, but I m not sure if I did.

Yes sir thanks a lot,but sir i am taking third nearest neighbour as well as nearest neighbour  with NEGF approach ,and in case of DFT how many carbon atoms i am supposed to take in calculation for more precise calculations.

Please give me some link of any paper sir which i can follow,I have calculated Conductance ,LDOS(local density of states and Ek relation where band gap is occurring.,what else i can calculate sir which are the unsolved problems in this case.

regards

DFT usually uses plane waves as a base and not atomic orbitals. Thus the problem becomes to estimate how many plane waves you need. However, there are codes which uses atomic orbitals, like SIESTA. The problem of how many neighbours you have to take in order to get a reliable result, is now transformed to the value of cutoff energy, which is used both in codes using plane waves, as well as SIESTA, although they have differnet meaning. More details you can find in manuals of the DFT codes.

Thanks a lot sir ,have you worked on g raphene nano ribbon sir?