How to get electrode coordinates for two probe system

[Anders Blom]

It really depends on where you are trying to enter the values. But generally no, you cannot set the electrode length to any value, it needs to correspond to a value that makes the electrode periodic.

[perfetti]

What do you mean by "extend the central region"? Should I extend it in the builder under device mode? I increased it even to 100% but there's no new value appearing in the electrode lengths.

If you import a device configuration into the builder, it will have a list of valid electrode lengths, select from the list.
If none of the listed lengths are large enough, you can extend the central region  and this will make it possible to use longer electrodes.

[perfetti]

Can you explain in more detail for " where you are trying to enter the values"?
How can get the value that makes the electrode periodic? I added half the lattice parameter but the structure still broken. i guess there's some allowable value gap in between.

It really depends on where you are trying to enter the values. But generally no, you cannot set the electrode length to any value, it needs to correspond to a value that makes the electrode periodic.

[Anders Blom]

What I mean is that I no longer understand what you are doing It started in the Custom Builder called "Bulk Junction" which I sent, but then I think maybe at some point you transferred the structure to the Builder or not... So, I'm lost, and cannot help unless you show more details, ideally a screenshot.

My advise it, don't change the electrode or surface lengths in the Custom Builder, just make sure the structure looks correct and that you have 4 or more metal layers in each surface (provided you have fcc 111). Then transfer to Builder, and there you can manipulate the length of the electrodes in a controlled way.

[dhurba]

This will be so much easier to do in ATK 12.2. We are currently make a completely new Builder, where this system is one of the test cases, which we are making sure is easy to build.

So, since that is coming out relatively soon, but not tomorrow, I decided to make the simplest solution possible (for me) which anyway works in 11.8.

The result is the quick-and-dirty Custom Builder attached to this post. How way to use it:

• First save this script on your computer.
• Then, drop it (the file) onto the "Custom" icon in VNL.
• You can drop any cubic metal like Cu or Au or Pd etc onto the "New electrode" dropzone (default is gold). It must be cubic because we need to cleave it. A simple extension would be to allow also ready electrodes; then one could also build pure nanotube or graphene junctions
• Now open another Custom Builder and select Nanotube from the menu. Choose the indices you want, and remember to repeat it so it's long enough.
• Then drag and drop the nanotube, using the script icon in the lower right-hand corner, onto the dropzone "Drop center bulk here".
• Now you can make some adjustments in terms of repetitions (in X/Y) distances etc so that you get something reasonable.
• Note that you can actually take any bulk system and put in the middle. So also some piece of graphene would work fine.

One thing you may want to "post-process" is to rotate the tube, or fine-tune it's position. This can be done in the Builder, by selecting all carbon atoms (right-click background, Select>Select by>Elements), and then use Transform>Rotate or Translate.



Let me know if you find any mistakes or problems with using it.

I want to use the above script to build a schottky diode by replacing the left electrode with Aluminum(110) and right electrode with Palladium/Gold or any other ohmic contact and drop a CNT(8,0) in the centre bulk ..Is my procedure correct .

[Anders Blom]

Currently my posted script will only build homogeneous structures where the left and right electrodes are the same. It's not entirely trivial to build heterogeneous systems like the one you envision because the XY unit cells for the two electrodes must be the same, and hence stretched if the lattice constants are not the same.

As mentioned, in ATK 12.2 we're improving things a lot, I will use your system idea to test if we have made it possible to set this up easily; it's an important type of system that we should support.

[anir]

This will be so much easier to do in ATK 12.2. We are currently make a completely new Builder, where this system is one of the test cases, which we are making sure is easy to build.

So, since that is coming out relatively soon, but not tomorrow, I decided to make the simplest solution possible (for me) which anyway works in 11.8.

The result is the quick-and-dirty Custom Builder attached to this post. How way to use it:

• First save this script on your computer.
• Then, drop it (the file) onto the "Custom" icon in VNL.
• You can drop any cubic metal like Cu or Au or Pd etc onto the "New electrode" dropzone (default is gold). It must be cubic because we need to cleave it. A simple extension would be to allow also ready electrodes; then one could also build pure nanotube or graphene junctions
• Now open another Custom Builder and select Nanotube from the menu. Choose the indices you want, and remember to repeat it so it's long enough.
• Then drag and drop the nanotube, using the script icon in the lower right-hand corner, onto the dropzone "Drop center bulk here".
• Now you can make some adjustments in terms of repetitions (in X/Y) distances etc so that you get something reasonable.
• Note that you can actually take any bulk system and put in the middle. So also some piece of graphene would work fine.

One thing you may want to "post-process" is to rotate the tube, or fine-tune it's position. This can be done in the Builder, by selecting all carbon atoms (right-click background, Select>Select by>Elements), and then use Transform>Rotate or Translate.

Let me know if you find any mistakes or problems with using it.

Dear Sir,
           I am trying to build a carbon nanotube transistor using the above script in which i have inserted a nanotube(5,0) in between Au(111) electrodes. As mentioned above,i followed the steps but at last it seems to have 4 layers of Au at the left surface and 3 layers at the right surface of the scattering region. Will this hamper my transport calculation..
                    thanking you in advance

[Anders Blom]

In principle it shouldn't be a big problem if there is enough screening. 3-4 layers are perhaps on the bit on the low side to consider the screening complete, however. But, I doubt it will be critical. Still, if you are concerned, it would be easy enough to add a 4th layer on the right in the Builder, just add 33.3333% of the electrode to the right surface.

[anir]

In principle it shouldn't be a big problem if there is enough screening. 3-4 layers are perhaps on the bit on the low side to consider the screening complete, however. But, I doubt it will be critical. Still, if you are concerned, it would be easy enough to add a 4th layer on the right in the Builder, just add 33.3333% of the electrode to the right surface.

Thank you for your generous reply..
But when i open it in the builder it already shows 33.3333% of the electrode to the right surface. So,can u just suggest me how to insert the 4th layer..

[Anders Blom]

Click the + sign

[anir]

Click the + sign

Thanks a lot..
Sir,i now have the structure of cnt(5,0) in between Au(111) electrode..
Do I have to optimize the structure to obtain proper results or without optimization also,i will get fair results in calculating transmission spectrum,DOS,etc..

[Anders Blom]

At least the distance between the tube and the surface should be carefully considered.

[anir]

At least the distance between the tube and the surface should be carefully considered.

Thanks for the reply,..
I am keeping a distance of 2.2A between Au electrode and Carbon Nanotube according to the published paper
J. Palacios, P. Tarakeshwar, and D. M. Kim, Phys. Rev. B 77, 113403
2008
Will that be fine in carrying out the calculation without optimization..

[Anders Blom]

It is at least good if you can motivate the choice of the distance, if you don't optimize it.

[anir]

It is at least good if you can motivate the choice of the distance, if you don't optimize it.

Ok..
then i will first try the above geometry without optimization and then thereafter i will try to optimize the structure and compare both the results...(for optimization i will need your help again later)
i will inform you what result i get...
thanks a lot for everything..