Messages

16

General Questions and Answers / Re: Nanowire direction

« on: January 2, 2018, 02:29 »

Do you know which direction is the [001] or [010] direction? If so, in my opinion, you can make this direction, such as [001] direction, to be the c direction of the nanosheet, by swapping the axis. Then, cut the nanosheet to form a nanowire.

17

General Questions and Answers / Re: About the repeatability and correctness of the calculation using ATK

« on: December 23, 2017, 16:17 »

I tried to write a script to make a k-point scan of the calculation by following the tutorial mentioned above. However, because I am not familiar with Python coding, I don't know how to change and update the parameters of the Calculator in the loop. There is something wrong with the script. Could you please help me with it? I do appreciate your kind help!

18

General Questions and Answers / Re: About the repeatability and correctness of the calculation using ATK

« on: December 23, 2017, 14:50 »

Thank you very much for your explanation! It's really helpful and I began to know what "Converge" means.

That means, if I want to carry out a calculation about a physical property, say, in this case, the transmission spectrum, I'd better check the convergence of this particular property in respect to the computational parameters which  would significantly affect the accuracy of the calculation, such as k-mesh density and  mesh cut-off. A way to check the convergence of such parameters is to take a scan. Is it correct?

Even for a 2D device, the k-mesh is defined as (1, kb, kc). Do I need to take a scan of both kb and kc or just take a scan of kb or kc? The former one must be a tedious work!

For the calculation of transmission spectrum, besides the k-mesh density and mesh cut-off, is there any other parameter that I need to check?

Thank you again for your kind help!

19

General Questions and Answers / Re: About the repeatability and correctness of the calculation using ATK

« on: December 23, 2017, 02:04 »

Thank you very much for your reply.

I do know that the accuracy (in particular in regards to k-point) of one calculation might be much higher than that of the other one. I am confused because I saw both the two calculations were converged to the same tolerance. I had thought that if the calculation could converge to a reasonable tolerance, it should be trusted and reliable. It seems that this view-of-point needs to be adjusted.  Now, I have no idea how to determine if the result is reliable----the "Converged" is no longe the criterion.

For this case, is it necessary to take a k-point scan as described in tutorial https://docs.quantumwise.com/tutorials/atk_transport_calculations/atk_transport_calculations.html ？Or just take the result with higher accuracy as the final result?

Thanks a lot again for your kind help!

20

General Questions and Answers / Re: About the repeatability and correctness of the calculation using ATK

« on: December 22, 2017, 16:16 »

Comparison of the two transmission spectrums...

21

General Questions and Answers / About the repeatability and correctness of the calculation using ATK

« on: December 22, 2017, 16:09 »

Dear ATK experts,

I am studying the transport properties (transmission spectrum) of a device using Huckel method. I have done two calculations with the same device configuration, the same bias voltage, while there are a little bit differences between the parameters for the calculations, such as k-point sampling, Poison solver, damping factor and so on. Both the two calculations were converged to the same tolerance. Attached are the .py file for the two calculations.

However, the transmission spectrums are quite different. The current in one calculation is about ten times of that in another calculation.

Who can tell me which one is correct and what’s wrong with the other calculation? How should I choose the parameters for the next calculation?

Thank you very much for your kind help!

22

General Questions and Answers / Re: About the convergence of the transmission spectrum calculation

« on: December 21, 2017, 14:28 »

Thank you very much for your help!

23

General Questions and Answers / Re: About the convergence of the transmission spectrum calculation

« on: December 20, 2017, 15:34 »

Thank you for your reply, Mr. Petr Khomyakov!

I can make sure that all the calculations are converged with the same tolerance. If so, can I compare two IV plots obtained with different parameter sets directly?

24

General Questions and Answers / Re: Image file generation from builder

« on: December 20, 2017, 04:28 »

You can use the Viewer to change the color of the background. You can also modify the text, lines, bonds and so son by Viewer. After that, I used to use Snipping tool to cut&paste/save the image to anywhere.

25

General Questions and Answers / Re: About the convergence of the transmission spectrum calculation

« on: December 20, 2017, 04:22 »

Another question:

I am studying the gate effect of a device. I have previously got some IV plots at different gate voltages with relatively less k-point sampling (less accuracy). However, it's hard to converge at some gate voltages. So I had to modify the parameters to improve the convergence, including the number of k-point sampling.

I don't want to redo the IV calculations with less accuracy since it's also very time consuming. But I am not sure if it is possible or reasonable to compare two IV curves obtained with different accuracy. Could you please help me with this question?

Thank you very much again for your kind help!

26

General Questions and Answers / Re: Extraction of polyhedron shaped nanoparticle

« on: December 19, 2017, 14:01 »

Normally, I will use the Snipping tool to cut off the image and save it. 

27

General Questions and Answers / Re: About the convergence of the transmission spectrum calculation

« on: December 19, 2017, 13:58 »

Dear Petr Khomyakov,

Thank you very much for your kind help! It's really helpful!

lknife

28

General Questions and Answers / About the convergence of the transmission spectrum calculation

« on: December 19, 2017, 10:38 »

Dear experts,

When calculating the IV curve of a device (I am using the ATK2015 and ATK2016, Huckel method), if I used the "IVCurve" block directly, sometimes it was found that the transmission spectrum did not converge at some specific bias values. Thus, I had to modify manually the parameters of the calculation, such as the damping factor, the history step and the Poison solver, and redo the transmission spectrum calculation bias by bias, which is very inconvenient. In some cases, it was very hard to converge (>1000 iteration steps). However, when changing to a suitable parameter set, it converged within 50-100 steps.

The are two questions about this problem:
(1) Is there any problem if the points of the IV curve were obtained using different parameters?
(2) Is there a better IVCurve block that can adjust the parameters automatically when it's hard to converge?

Thanks a lot for your kind help!

29

General Questions and Answers / Re: how to read the result calculated using newer version ATK?

« on: December 1, 2017, 08:25 »

BTW, I want to get the current from the transmission spectrum. Also, I can read the .log file calculated before but I cannot find the current information from the file.

30

General Questions and Answers / how to read the result calculated using newer version ATK?

« on: December 1, 2017, 08:22 »

Dear experts,

I have a permanent license of ATK2015 and temporary license of ATK 2016. I did some simulation with ATK2016 but it now expired and the renew of it is on the way. Now, I wanted to read directly some of the results calculated before using ATK2016, such as transmission spectrum, with ATK2015 but failed. Since I don't want to redo the simulation with ATK2015, can anybody here help me with this problem?

Thank you very much for your kind help!