construction details of Graphene on hexagonal boron nitride bilayer system

[Abe]

sir,
    i am trying to obtain the results  by performing density functional calculations for
bilayer graphene/h-BN system in tetrahedron method using ATK.I took Z=16 A,X=2.456 A.
But they were used the same thing using QE.In QE z dirction is fixed but in the case of ATK x direction is fixed.If i used the same Z and X direction value in ATK i cant able to fix 3 layers.could you help me how to construct 3 layers.i constructed the same thing using ATK but i changed Z&X direction values.but i didnt get the same curve.

[zh]

Both billayers of graphene and BN are in the hexagonal lattice. Hence the simple way to model the bilayer graphene/BN system is the use of the hexagonal lattice, rather than the tetragonal lattice.

[Val]

thank you for your reply.i built the graphene from graphene nanoribbon option instead of ribbon i choose sheet option.but when i calculating energy it have some energy value.so i thought i wont be a 2D graphene.could you tell me how to construct 2D graphene using ATK.

[zh]

The structure of graphene is already included in the "Database" tool of VNL10.8.

[donmbringer]

Hi. But it seems that bilayer model could not be built directly from graphene model. I tried to repeat it from c direction for 2, and pull the second layer close to the first. It seems that this does not work. Could you please tell me the reason and the solution?

[donmbringer]

The structure of graphene is already included in the "Database" tool of VNL10.8.

Hi,

May I ask, how I can build the electrode using Miscellaneous if the cell unit is a parallelogram, such as graphene, rather than a rectangle.

 It seems that if  I build an rectangle-sized electrode which is big enough to cover the cell of graphene. The result is not correct.

[Anders Blom]

It's ok for the regions to extend outside the cell, those parts will be automatically cut out of the calculation.

[donmbringer]

Dear Dr Blom,

Many thanks for your reply. I tried this problem several times. The software is very effective to simulate the parabolic shape.

However, it seems that the voltage apply is not sucessful.

I applied 4V/nm, which should be able to open the band gap, but in software, it does not. What is the reason?

[Anders Blom]

Try 20 V, or more. I'm not sure the field can be normalized the same way as in an experiment. The atomic layers shield the field, so you may not have the same field in the middle.

[donmbringer]

Dear Dr. Blom,

It seems that 52 Volt does not work either. I build the bilayer graphite with lattice parameter c = 15A. Interlayer distance is 3.34 A. Then, as the attachment shown, I add two matel layer using spatial regions, which are separated by 13 A. To create a electric field of 4V/nm, we need the potential different to be: 4 * 1.3 = 5.2 V. Therefore, I set one side as 0, another as 5.2V. The bandgap is not opened.

I even tried 52 V, the bandgap did not changed as well. Where am I wrong?

[Anders Blom]

What about other parameters? The geometry seems fine, but what about numerical settings?

[donmbringer]

I just directly import the file I put in the last attachment into the Script.

Do you mean simulation parameters?

I just added Calculator, chose Huckel, changed k-point to 8, 8, 1, and changed basis set to Cerda.carbon.

then I chose bandstructure, change points to 200, and route to G K M G.

Then I sent it to job manager.

[Anders Blom]

The calculation must be self-consistent, that is the most important point. It's better to post the full script, then we can check all details.

[donmbringer]

Hi Dr. Blom,

Sorry, I couldn't find the way to export the full script, since the format I can choose is only "all file". I don't know the reason.

So I just copy every step I made (after sending the .py file to the script generator) as the figures shown in attachment.

If you still need the full script, could you please tell me how to do that? I am a beginner for this software.

[Anders Blom]

In the Scripter, use the menu File>Save or click the Save icon or press Ctrl+S.