QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: Val on January 28, 2011, 04:51

Title: bilayergraphene
Post by: Val on January 28, 2011, 04:51

sir,
     i want to calculate bandstructure of bilayer graphene with one particular external voltage.I thought in two probe system only we can able to apply external voltage.but in the case of two probe system we cant able to find bandstructure.with this i attached my script file and required bandstructure of bilayergraphene.could you help me how to get the bandstructure of bilayergraphene.

Title: Re: bilayergraphene
Post by: kstokbro on January 29, 2011, 08:12

1. Select graphite in the data base
2. send it to the builder and adjust the lattice C vector to 15 Å in order not to have any interaction in that direction
3. send it to the script generator:
             use 8,8,1 kpoints
             add bandstructure, set the symmetry points to the route you want, G, K, M
4. calculate

You might also want to relax the structure

Title: Re: bilayergraphene
Post by: donmbringer on August 6, 2012, 16:03

Hi. I am a new user of ATK. May I ask, how to "adjust the lattice C vector" in builder?

Title: Re: bilayergraphene
Post by: donmbringer on August 6, 2012, 16:07

I mean, if directly changing the lattice parameters to 15A, this will increase the space between every single layer. But, we need to produce bilayer, so we need to adjust two layer as a period (which have a very close space), and make each period spaced for a large distance. How should I do?

Title: Re: bilayergraphene
Post by: Anders Blom on August 6, 2012, 16:32

In the lattice parameter widget, choose to keep Cartesian coordinates, rather than fractional.

Title: Re: bilayergraphene
Post by: donmbringer on August 6, 2012, 17:13

Many thanks. It seems that it is correct this time.

But. I have one more question. Since in this way, the model is period in c direction (z axis), how could I apply a vertical electric field (such as 2 Volt) in this case?

Title: Re: bilayergraphene
Post by: Anders Blom on August 6, 2012, 17:26

I assume you are interested in the transverse field, and how it opens a band gap, not the lateral transport in the graphene sheets. For that you should insert metal regions at top and bottom, and apply the field between them.

Title: Re: bilayergraphene
Post by: donmbringer on August 6, 2012, 17:34

Yes. This is exactly what I need to do. Is it correct to follow what is shown on this tutorial：http://www.quantumwise.com/publications/tutorials/builder/172-building-a-molecular-junction-au-dtb-au？But if we do this, the model will be transformed to a device, which make it not possible to calculate the band structure,

Or, there are some different ways to build the metal surface and apply the electric field?

Title: Re: bilayergraphene
Post by: Anders Blom on August 6, 2012, 19:09

Yes. You should add metallic "spatial regions" above and below the bilayer structure, like in http://quantumwise.com/forum/index.php?topic=1561.msg7802#msg7802
You can add these in the Builder, under "Miscellaneous" tools.

Title: Re: bilayergraphene
Post by: donmbringer on August 6, 2012, 22:47

Hi Dr Blom,

I did what you said before. I choose the parameter as shown in the attachment,  which has the potential of 4V/nm but it seems that there is no band gap. This is different from the literature "Energy band-gap engineering of graphene nanoribbon" on PRL, in which 4V/nm is totally enough for bandgap opening. Could you please tell me why I am wrong? 

Title: Re: bilayergraphene
Post by: Anders Blom on August 13, 2012, 00:08

For anyone else surfing this thread, the solution is provided elsewhere: http://quantumwise.com/forum/index.php?topic=996