[Wannier] adding two different systems or merging two systems to form one

[Giovanni Pizzi]

Dear Zeina,
one possibility is to simulate the "merging" region only, together with enough graphene on one side and CNT on the other so that the hopping energies and onsite energies far away from the interface are the same of the pristine graphene and CNT only.
You can then use the correct hopping and onsite energies for each region (those in the intermediate region from this last simulation, and the hoppings far away from the two pristine simulations). This can be done with Wannier90 or with other codes that calculate the transmission given the proper Tight-Binding Hamiltonian.
In practice, things can get more complicated, e.g. if there is charge accumulation that can shift the relative hopping energies of the two materials, but this depends on the specific material.

Otherwise, if the global system is not too big, you can try to simulate directly the whole system. Just remember that the code still assumes periodic boundary conditions in the 1D direction, so you will probably need to create, e.g., a system with two junctions (from CNT to graphene and then back to CNT); however in this case, you will measure the conductance through both junctions, that may or may not be what you want.

Best,

Giovanni


--
Giovanni Pizzi
Post-doctoral Research Scientist
EPFL STI IMX THEOS
MXC 340 (Bâtiment MXC)
Station 12
CH-1015 Lausanne (Switzerland)
Phone: +41 21 69 31124




On 13 Nov 2014, at 22:04, Zeina Al-Dolami wrote:

Dr. Arash and Dr.Giovanni,
Thanks so much for your help. It worked and I got what I needed :)  I have one more question that I am not sure about its answer. My question is that what should I do to include or merge two systems together? To explain, let's assume that I would need to find the quantum conductance for a system that has a  carbon nano tube and a sheet of graphene. Also, let's assume that I have already calculated the quantum conductance when they are separated, i.e. each one is a system by itself. Now, I need to find the quantum conductance for the whole system that has both in a device. Would it be just identifying the positions and k points for that whole new system or there is something else that I need to consider to investigate the difference between bringing them together in one system and separated? Any answer or hint is greatly appreciated. Many thanks in advance

Zeina
PhD candidate in MEPH
University of Arkansas
Fayetteville, AR 72703




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