Messages

1

General Questions and Answers / question on transistor simulation tutorial

« on: October 11, 2020, 17:16 »

hi everyone,
I try to simulate graphene nanoribbon transistor ( z shape ) as mentioned in the tutorial. I do some calculations and I got a problem in the interpretation of what is happening in this tutorial. I would wonder if someone can help me. ( in the device3.py in this tutorial there is a hydrogen atom which should be removed.)

The result shows a very low transmission in -1 to 1 eV range (Vg=0) using GGA-SZP which is in good agreement with Armchair GNR bandgap IF we consider it very long along z-direction, but in this tutorial, we are studying an armchair in z shape which is very short and if we just split this device3.py and add 20 angstrom to the center and getting bandstructure we will see that the bandgap is reduced to 0.2eV which means that due to quantum confinement along z-direction the new (z shape armchair ) has small bandgap which is not in agreed with the transmission results.
I can not understand the channel is considered as a  long armchair ? or is it a small one? or due to very little subbands forming a 0.2 eV gap in this quasi-quantum dot armchair shape structure! we can not get the transmission around it?

thanks
Rose

 

2

General Questions and Answers / Question on using gate voltage

« on: June 11, 2020, 15:56 »

Hi,
I am trying to simulate the following paper for the sake of learning,
https://doi.org/10.1002/adfm.201402904

I can regenerate Figure 2 in this paper and it perfectly matches, however, I can not regenerate the Figure 3d results.

While the transport in Vg=0 is achieved properly, the results in Vg=20 is not regenerated. I also check for Vg=40V but still, nothing can get similar to the mentioned paper also checked both Drikhle and Newman's condition in the gate direction but still not get any match for gate voltages. I read most of the tutorials on the gate voltage but can not understand why I can not regenerate the voltage gate results.

 I attached the input file. I would wonder if it would be possible to guide me to find my mistake.
sincerely
Rose

3

General Questions and Answers / question on the gate voltage

« on: December 17, 2018, 13:39 »

hi,
I just reading the tutorial

https://docs.quantumwise.com/tutorials/graphene_nanoribbon_device/graphene_nanoribbon_device.html#graphene-nanoribbon-device

on the gate of graphene nanoribbons and I do not understand when I apply -1V as the gate voltage, what is the zero reference that the value of the gate is -1V compared with it? Is it the applied zero voltage reference that considered for both electrodes(source and drain in the case of FET)? 
thanks
Rose

4

General Questions and Answers / Re: atk jump out in gate transport calculation.

« on: May 9, 2018, 12:31 »

Hi,
Thanks. I just emailed the log and Py
thanks
Rose.

5

General Questions and Answers / atk jump out in gate transport calculation.

« on: May 9, 2018, 08:04 »

hi everyone,
I am working on transport properties with gate but as I submit the script for job manager and run it (either parallel or serial) the atkpython stop working without any notification and then job finished without error. It happens when loading left electrode and in the log
+------------------------------------------------------------------------------+
|                                                                              |
| Left Electrode Calculation  [Started Wed May 09 09:37:07 2018]               |
|                                                                              |
+------------------------------------------------------------------------------+
+------------------------------------------------------------------------------+
|                                                                              |
| Storage of orbitals in real space requires    55 MB.                         |
|                                                                              |
+------------------------------------------------------------------------------+
+------------------------------------------------------------------------------+
|                                                                              |
| Real space grid sampling is (295, 53, 46) in a, b, and c directions.         |
|                                                                              |
+------------------------------------------------------------------------------+
+------------------------------------------------------------------------------+
|                                                                              |
| Storage of atomic core grids requires     5 MB per grid                      |
|                                                                              |
+------------------------------------------------------------------------------+

then it stopped and finished without any error on the output....
Is it from my structure? since when i completely remove the gate, the structure work and calculate the transport.
What is happening here?

I will send the python of structure if needed in private.

thanks
Rose

6

General Questions and Answers / Running atk on linux

« on: January 9, 2018, 13:24 »

hi,
I am recently shifted to Linux version of atk and the system do not support the visual so I want to run using command but each time I run following command, I got to an error: "  QXcbconnection: Could not connect to display"

mpirunt -np 1 atkpython <test1.py> test.log

the log file is empty. The test1.py is generated by windows version of VNL.
what should I add to my code or commands to overcome this problem?
thanks
Rose

7

General Questions and Answers / on linear response approach for finding hubbard

« on: December 18, 2017, 16:11 »

Hi all,
I would wonder if it is possible to apply linear response approach (Phys. Rev. B 71 035105) to find Ueff in hubbard of d orbitals using atk.
thanks
rose

8

General Questions and Answers / Re: problem in optimization of molecule

« on: August 3, 2017, 10:59 »

Hi,
Thanks for the response.

 I thought it might be that so I used a stable reported structure of CeO2 and used DZP- SGGA- PW- with Hubbard 4 on Ce. But the system is reducing bonds so that all atoms are compact to each other.... I really can not understand what is going on that such odd behavior happens. The attachment is the input file.  Would it be possible that this related to charge or sth like that?
thanks
Rose

9

General Questions and Answers / problem in optimization of molecule

« on: August 2, 2017, 17:12 »

Hi everyone,
I want to find the optimized structure of attachment molecule and surprisingly after few step in optimization the system collapses and everything attract to each other?
why does such thing happen?
thanks
Rose

10

General Questions and Answers / unknown warning in IV curve

« on: July 25, 2017, 16:20 »

Hi everyone,
I am calculating transport properties and I got a warning as follow:

IV-Curve Calculation
The current will be calculated at 10 points between 0.000 to 2.000 V
Note: the Current has already been calculated at 0.000 V
Each bias point will be calculated using 1/1 MPI process.
Bias Point   Process group  Log File
0.200                               0          E:/SavedVNL/... <==  WARNING : Truncated content
0.400                               0          E:/SavedVNL/... <==  WARNING : Truncated content
.....
2.000                               0          E:/SavedVNL/... <==  WARNING : Truncated content

and then the system is frozen at these points but the ram show the working but nothing type.
What does it mean?
Thanks
Rose

11

General Questions and Answers / Re: question on validation

« on: July 19, 2017, 16:16 »

Hi
Thanks for your answer. Yes, I got that part from the paper, however, the Figure in this tutorial is up to 1eV which as I got is far more than 1THz. So I think the question is still stand. Does WBL still correct in this 1eV energy?
Thanks
Rose

12

General Questions and Answers / question on validation

« on: July 18, 2017, 15:27 »

Hi ,
regarding the tutorial:
http://docs.quantumwise.com/tutorials/low_level_entities/low_level_entities.html

I am really interested in the impedance response of CNT that mentioned there.

Does the wide-band limit is validated in high frequency? If yes why? If no up to which value we can say that the wide band limit is valid?
thanks
Rose

13

General Questions and Answers / Re: On Fermi Level

« on: June 18, 2017, 11:31 »

Thanks.
I check your idea and improve the k point sampling and I got various type of Fermi level in the band gap. Some show n-type (small values of k point) and some show p-type (large number of k) characteristics. Interestingly the sample did in the quantumwise as the example of transmission of mos2 present slightly p-type characteristic while it is not mentioned explicitly in the text but it can be concluded from the figure.

I would wonder which technique of doping in atk (Explicit charge/Atomic compensation charges) is more effective in considering n-type mos2 as the channel of a transistor? how can I apply it?

thanks
Rose

14

General Questions and Answers / On Fermi Level

« on: June 13, 2017, 14:40 »

Hi
it is well-known that mono-layer MoS2 and WS2 can affected by the substrate and may show p or n type behavior, but, in pristine suspended structure, MoS2 has n type characteristic while WS2 shows p type. I try to find the bandstructure of both MoS2 and WS2 but in most cases i got intrinsic ( Fermi at the center of band gap) or sometimes p type one. What should I do to simulate this natural n-type characteristic of MoS2?
p.s: i knew about the doping option in atk but this is natural n-type characteristic not adatom of functionalization effect.

thanks
Rose

15

General Questions and Answers / Re: converge problem all again.

« on: March 21, 2017, 08:53 »

Hi,
I tried to use higher mesh density but I can not still got the converged.
I did not got the comment on the defect. I want to find the pristine current-voltage characteristic and then find the defect one. Is there any other way so I can find the IV curve for the pristine, then?
Any idea how can i got the convergence for finite bias in pristine one?
thanks
Rose