Messages

1

General Questions and Answers / Re: Total energy sign in ATK

« on: October 7, 2013, 13:53 »

Thanks.

2

General Questions and Answers / Total energy sign in ATK

« on: October 7, 2013, 13:04 »

I simulated a BN nanotube in ATK. Tried to find the optimum bond length by comparing a few total energies in different simulations. However confused a bit. It might be a simple question but is the bond length with the total energy -12542.8760 eV or -12542.6181 eV better? Which is closer to the lowest energy point? Do I have to compare the absolute values or with the (-) sign? Thanks...

3

General Questions and Answers / Re: Transport properties of a zigzag nanoribbon tutorial

« on: October 4, 2013, 21:44 »

I also did the polarized and unpolarized transmission spectrum calculations as attached. Spin up and down transmissions are different as can be seen from fig 1 although bandstructure of up and down stated were overlapped as in the tutorial. Why up and down transmissions are different and what's the relation of them to the unpolarized transmission shown in the latter figure. Thanks a lot.

Note: And how to decide to include spin polarization for a device? Is it just try spin polarized and not and compare each other?

4

General Questions and Answers / Re: Transport properties of a zigzag nanoribbon tutorial

« on: October 4, 2013, 09:59 »

Thanks for the reply.

In the mentioned tutorial on page 8, BlochState dialog box has the optin "None" for the spin but in ATK 12.8 there are only spin up and down options there. How can I replicate the tutorial since when I select spin up or down, the resulting states are different from those given on page 10?

Best
Jimmy 

5

General Questions and Answers / Transport properties of a zigzag nanoribbon tutorial

« on: October 3, 2013, 10:48 »

Hi,

I replicated the zigzag GNR tutorial (Transport properties of a zigzag nanoribbon) and obtained the same results. However, I'm a bit confused. Because I came across a paper mentioning spin-resolved bandstructures and bandgaps for ZGNRs (http://www.nature.com/nature/journal/v444/n7117/abs/nature05180.html). Is it possible to obtain spin-dependent bandstructure of the GNR in the tutorial in ATK? There seems a bandgap when spin-polarized bandstructure is drawn according top this paper.

Thanks in advance...
Jimmy

6

General Questions and Answers / Re: Transmission question

« on: September 29, 2013, 09:14 »

You can at least compute the effective potential and compare it at zero and finite bias. You can subtract them to see the potential change induced by the bias.

Hi again,

I did calculate the potential profile along z direction as attached. Applied voltages are 0.25 and -0.25V at the leads. This is for a metallic CNT. It seems like the potential jumps to 0.3V near the left interface and to -0.27V at the right interface. Considering the applied voltages are 0.25V and -0.25V, is there an error becase the potential jumps higher than the applied voltages?

Thanks in advance.

7

General Questions and Answers / Re: Transmission question

« on: September 20, 2013, 09:16 »

Hi again,

I also thought to check the variation of the average electron density along the transport direction. I tried to modify the code you gave in one of the previous topics: http://quantumwise.com/forum/index.php?topic=2389.msg11132#msg11132 but unsuccessful to modify properly 

Any help would be appreciated. Thanks a lot.

8

General Questions and Answers / Re: Contact resistance of graphene-Ni interface

« on: September 20, 2013, 09:09 »

Thanks, I'll give a try for the small voltage values as you pointed out...

9

General Questions and Answers / Re: Transmission question

« on: September 19, 2013, 16:35 »

I'll try, thanks.

10

General Questions and Answers / Re: Transmission question

« on: September 19, 2013, 15:55 »

Thanks again, moreover in ATK is there any other way of visualizing potential scattering effects other than looking at T(E). I mean: can the change effective potential as the applied voltage increases, or some other parameter also give opinion, at least qualitatively, on the potential scattering mechanism? So that the variation of the transmission spectrum for different devices as the applied voltage increases can be interpreted using simulations.

Thanks a lot.

11

General Questions and Answers / Re: Transmission question

« on: September 19, 2013, 12:11 »

Thanks a lot. However does ATK model the scattering effects?

12

General Questions and Answers / Transmission question

« on: September 19, 2013, 09:50 »

Hi all,

I just wonder why the simulated transmission spectrum decreases in most of the structures in ATK when the applied voltage increases. I tried for nanotubes, graphene and molecular junctions. The transmission decreased for all these.

Thanks in advance.

13

General Questions and Answers / Re: Simple optimization example

« on: September 19, 2013, 09:48 »

Thanks. It worked.

14

General Questions and Answers / Simple optimization example

« on: September 10, 2013, 12:25 »

Hi,

I'm trying to make an optimization to a graphene sheet with the code attached. However, there seems ony 1 optimization step even if I change the optimization force criteria from 0.05eV/A to 0.03 or 0.01. The initial atomic positions do not change after the code is run as you can see from the output file. Is there a problem with the code, your help is appreciated.

Thanks...

15

General Questions and Answers / Compute total charge

« on: July 31, 2013, 10:41 »

Hi all,

How can I compute the total charge inside the scattering region when I do a 2-probe device simulation? The electron density is exported as a cube file which I don't know. Can it be done inside ATK in Python language?

Thanks a lot.
Jim