Topics

1

General Questions and Answers / The thermal considerations of QuantumWise

« on: September 10, 2013, 17:38 »

Dear everyone,
        I am working on a case that CNT-Bi's conductance properties VS temperature. We optimized the same structure at different temperatures and then calculate their transmission spectrum. However, the structure after the optimization looks ridiculous as the metal atoms go far away from the carbon nanotube. And the transmission coefficient has no particular trend, as it goes down from 300K to 403K, but goes up from 403K to 423K.
       I am not sure if the QuantumWise software considered the temperature effect on properties, and to which extent?  Maybe it's not a proper way to try to pry the temperature effect on this software?
       On the other side, my device may have problem and any picky advice is very welcomed.
       Thanks very much!

2

General Questions and Answers / broken bonds in carbon nanotube when optimization

« on: September 10, 2013, 17:12 »

Hi all!
I am optimizing a carbon nanotube clamped with 20 copper atoms in it. However, in the process of the optimization, the carbon nanotube has been broken and copper has been embedded into the carbon nanotube.
I am not sure this situation is reasonable, since the carbon-carbon sp2 bond is said to be stronger than that of diamond, so why the copper atoms can break the c-c bond? Is the carbon nanotube generated in this software give consideration of the physical properties of real carbon nanotube? If so,what mechanism is underlying? Hope anyone could clarify that for me. Discussion is also welcome.

The relaxation trajectory is attatched. Thanks.

3

General Questions and Answers / VNL error

« on: March 11, 2013, 16:50 »

Dear Everyone,
        I was doing a structure relaxation for a unit cell, and I was recording its relaxation trajectory. However, I got this error when I was trying to view the trajectory file:

The following error message was generated when running the script:
Not all of the given cartesian coordinates have three coordinates.
Typically this is caused by a syntax error or a spelling mistake; the message above should be helpful in correcting the issue in such cases.
If you believe the error is caused by VNL itself, please report the issue to QuantumWise, and make sure to include the traceback (click "Show Details...") and the script.

Could anyone explain this error to me, and tell me if my relaxation result is correct with this error happening?

4

General Questions and Answers / Cross section area measurement

« on: February 25, 2013, 17:00 »

Dear Everyone,
       I've a little problem here:
       I want to calculate the cross section area of a certain part in my device, however, it seems to be impossible in ATK. I want to know if there's any way to get the cross section area of any part, using the length scale of vnl.
       Attatched is a picture of the cross section. My problem is like if I want to get the cross section area of the CNT,what should I do.
       Thank you!
       Best regards.

5

General Questions and Answers / Discontinuous two probe structure

« on: November 19, 2012, 20:07 »

Dear Everyone,
        I am having a problem. I relaxed a unit cell, and it get uneven edge after relaxation.
        I was trying to build up a two probe device using this unit cell, but it appeared to have a gap at the electrode/central part.
        I adjusted the electrode size  and the central part a little, but nothing useful happened.
        Could anybody give me any advice about fixing this problem? Thank you.

6

General Questions and Answers / Will the PBE underestimate the bandgap?

« on: October 9, 2012, 20:33 »

Dear every one,
       I am reading some literature and it said PBE may underestimate the bandgap of a material and may cause wrong conlusion, would that be true? Or how much would the error would be? Thank you.

7

General Questions and Answers / Back Engine Exception : Diagonalization error

« on: September 29, 2012, 15:50 »

Dear everyone,
       I am trying to calculate the total energy of a system, however, I've always got this error:* Back Engine Exception : Diagonalization error, overlap matrix not positive definite. This may be caused by atoms that are too close to each other or situated in equivalent positions, or (in the Extended Huckel model) a too low value of interaction_max_range
** Location of Exception : mathutils.cpp:1084



This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.
+----------------------------------------------------------------

the input script is attatched. Could anyone give me any advice?
      Thank you.
      Best regards.

8

General Questions and Answers / Relaxation refused to converge

« on: September 21, 2012, 21:41 »

Dear Every one,
       I am trying to relax a CNT(10,0) with 10 copper chains on it. However, after long time relaxation, the structure failed to converge, and gave a meaningless structure at the end(not converged).  
       I am wondering if you can pointed out one way for me to get this structure converged, if not, can you give me some advice to let the CNT with 6 chains successfully relaxed?  
       The input script for CNT with 6 chains/10 chains have been attatched, the trajectory file for the CNT with 10 Cu chains is too large to upload, but I can send it by email at asking.
      

9

General Questions and Answers / Band gap in metallic carbon nanotube

« on: July 26, 2012, 21:59 »

Dear every one,
       I am calculating the bandstructure of cnt(5,5), and it should be very easy. However, I always got a small bandgap near Fermi level in the bandstructure.
       I used k point =30,  50, 100, and it doesn't change much. I keep using GGA, PBE,  since I've no idea how I should set up about other exchange-correlation function.
      My input script and the bandstructure are attatched. Any advice should be appreciated.  I just want to eliminate this gap, or at least understand it.
      Thank you!

10

General Questions and Answers / Plotting Bandstructure in a certain range

« on: July 19, 2012, 22:12 »

Dear Everyone,
       I have a very simple question: I want to plot the bandstructure via graphical software like Origin, however, when I export all the data , and import them into origin, I found out that I cannot adjust the range. I got all the bands in [-20,20], however, if I want only the bands in [-2,2], I could do this by deleting a bunch of data, but unfortunately usually one would miss some lines. So this wouldn't be practical.
       I am hoping anyone could give me an advice on how to replot the bandstructure in a small range ?
       Thank you! Best regards.

11

General Questions and Answers / Transmission spectrum with trench

« on: July 10, 2012, 22:37 »

Dear Everyone,
        I am sorry to ask so many questions, but I couldn't figure it out by myself, and usually I ask after I tried a lot.Still thanks for your time!
        I got an transmission spectrum like following. It has a lot of trenches in it. I checked the electrode length, and it's OK. And I changed the exchange correlation from PZ,LDA to GGA,PBE, but it has no big effect.
        1)I am not sure if I got the right transmission spectrum?
        2)What's the difference between PZ,LDA and GGA,PBE? Will it affect a lot on the result? For my case, PBE,GGA method is 10 times slower. But I see all others they are using this method.
        
        

12

General Questions and Answers / Strange optimized geometry

« on: June 27, 2012, 18:01 »

Dear Everyone,
       I have a big trouble now: I am optimizing the geometry of my two probe device. It's a very basic one, composed of one copper chain absorbed on carbon nanotube, and then I performed a full device configuration optimization of my setup. However, I found that my optimized geometry is much different from what people got in literature.
        My initial geometry is like this: 1.jpeg
        While my after geometry is like this:
         2t.jpeg.
        While in the one in literature, they usually get geometry like this:
        3.jpeg.
        
        I know there are surface layers in my structure, and in ATK they constrained the electrodes automatically, however, I didn't expect such a result. I am not sure if this optimization is meaningful or not, since it looks much different from others, and I don't know if  the following properties calculation from this optimized structure are reliable.
        Any one giving advice is very appreciated. Thank you very much.

13

General Questions and Answers / I-V curve wouldn't converge at larger bias

« on: June 25, 2012, 16:38 »

Dear all,
       I am trying to calculate the conductance of a two probe device, and I have optimized the distance between the electrode and the central part. Then I throw it to I-V curve calculation. However, The scf loop would only converge for the first two voltage biases as 0V, and 0.5 V, and it wouldn't converge  for the following 1 V and larger bias.
       I am not sure if my setting was wrong, or if there's a possible solution for this? Could I just use the two points of 0V and 0.5V, and get a conductance?
       Any advice would be appreciated.    
       Best regards.

14

General Questions and Answers / i-v curve algorithm

« on: May 11, 2012, 16:29 »

Dear everyone,
       i am calculating the I-V curve following the I-V curve and voltage drop tutorial,and i did the scf calculation for each bias voltage, and stored the nc file seperately. In the scf calculation, I used krylov as device algorithm.  
       And in the step of computing the transmission and voltage drop for each case, I used the script and changed it a little bit according to the notes.  The only thing I am worrying about is : I didn't find the device algorithm in the analysis script, and it only shows up as the configuration.calculator, and I just leave it as it is.
      I am not sure if it's still using krylov algorithm? Cause it's really very slow in this step.
      

15

Installation and License Questions / License error on ubuntu

« on: May 2, 2012, 17:32 »

I am trying to launch the QuantumWise software on ubuntu 11.10.  I input the command : atkpython, however, it gave me a licence error as follows:

license error:(internal:719 feature:VNL)
(err:9) feature not found.

It happened on both previewed edition and the demo edition.

Any advice is appreciated.