Messages

1

General Questions and Answers / Re: The computation failed to converge when the negative bias was applied

« on: December 1, 2010, 15:32 »

Thanks a lot, Blom!
I have increased the K point sampling and the computation looks better in approaching the convergence.

2

General Questions and Answers / The computation failed to converge when the negative bias was applied

« on: November 30, 2010, 14:02 »

Hi. everyone!
Hi, Blom! I have also tried to search the forum for the topics similar to the following problem but there are no findings. Sorry! 

I am calculating a two-probe system using 2008.10 version. The I-V characteristic under the positive bias has been computed successfully and effortlessly. However, the computation is very difficult to converge when the negative bias is applied on the system. Then I changed the electron temperature from 300K to 500K, and the problem was still existing. Can anyone tell me what is the reason and how can I do to solve the problem? Thanks in advance!

3

Future Releases / Re: What is your Linux distribution?

« on: November 12, 2009, 04:16 »

My linux version is Redhat Enterprise WS4, but I use VNL/ATK in windows XP 

4

General Questions and Answers / Re: Is it reasonable that the current is different?

« on: September 10, 2009, 10:25 »

Thank you,zh
The I-V calculation in 1000k, 500k and 400k took less than 20 steps samely. But in 300k it exceeded more than 200 steps and there was no convergence tendency yet. Furthermore, the charge is large. I know the temperature may change the current. But it looks that the difference is too large. So, I am wondering, too. 
I will check the transmission spectrum in various temperature. Or I'll change the basis set or K points, etc.
Thank you again. I will post here when I get the new results.

5

General Questions and Answers / Is it reasonable that the current is different?

« on: September 10, 2009, 07:55 »

  Hello!
  A question again. 
  When I run I-V calculation, I found it was hard to converge under high bias after many steps. The electrode temperature is 300k. I think the current should not be zero, even if the job can converge, because the charge in the logwindow keeps large. For the convergence problem, I stoped the calculation. Then I changed the electrode temperature to 1000K and re-calculated the current. The task terminated normally in a short time and the current is close to zero. It is all close to zero though the temperature is changed to 500K or 400K. So I confused very much. Which result can be believed?  Is it reasonable that the current has different value apparentlly under different temerature or other conditions?

  Thanks in advance!

6

General Questions and Answers / Re: should I run SCF calculation separately under various method parameters?

« on: September 10, 2009, 04:31 »

Thank you, zh. Thanks for your detailed explanation.

7

General Questions and Answers / should I run SCF calculation separately under various method parameters?

« on: September 9, 2009, 17:01 »

Hello all!
I want to compare the difference of the zero bias transmission spectrum(TS) under various method parameters, for example K-point samping. The SCF calculation with specific K-point(1x1x500) has been executed and I used it to run the corresponding TS. Then I change K point to another one. Should I re-calculate zero bias SCF in this K-point setup firstly before the new TS calculation will start?
In other words, is the zero bias SCF result in specific parameters always useable for all analysis calculation even one has changed the method parameters?
One more question, in the case above mentioned, should the K-point be samed in "method" with in "analysis" when one calculates TS? I know the post "About the Number of k-points ?" in this forum, but I am still confused a bit.  Which one can bring more effect on the transmission results? 
Best regards!

8

General Questions and Answers / Re: A question about MPSH calculation：some eigenstates can't be obtained

« on: August 31, 2009, 16:54 »

It looks very attractive to use script language to configurate the calculation conditions. I will try it following your words.

9

General Questions and Answers / Re: A question about MPSH calculation：some eigenstates can't be obtained

« on: August 31, 2009, 16:21 »

Usually, I used VNL to create new input file, and looked through the scripts sometime. I will try on how to use the checkpoint file.
Thanks!

10

General Questions and Answers / Re: A question about MPSH calculation：some eigenstates can't be obtained

« on: August 31, 2009, 15:37 »

It should not take more time, provided you use the functionality to restore the checkpoint file and compute the MPSH states from that. In that case the overhead should be minimal since you do not need to re-run anything, i.e. you run the SCF loop once only, and then use the converged state to perform various types of analysis, like the MPSH states or compute the transmission, etc.

Restoring the checkpoint file can be set up from VNL, although it's often best to do it directly in a script, using copied code generated by VNL.

Oh lord, I actually don't know the function of the checkpoint file and never used it before. According to what you said I have wasted much time. Thank you very much for the useful advice. I will learn how to use checkpoint file and hope you give me guidance if I encounter some trouble.

11

General Questions and Answers / Re: A question about MPSH calculation：some eigenstates can't be obtained

« on: August 31, 2009, 14:32 »

Thanks for your reply, dear Blom!  
In fact I have guessed the reason and have dealed with it like your reply. Of course, I must use more times to complete the calculation.
thanks again.

12

General Questions and Answers / A question about MPSH calculation：some eigenstates can't be obtained

« on: August 31, 2009, 06:55 »

Hello,everyone. 
I found that my probe-system calculation can terminated normally when the quantity of the MPSH eigenstates was less than 17, however, can not terminated normally when the quantity was 18 or larger.  In the case of the latter, the *.vnl file can still plot normally in the Nanoscope but there are only 17(index from 0 to 16) eigenstates, and other eigenstates above the 17th can't present in the nanoscope list.  The error message in the output log is as below:

Traceback (most recent call last):
  File "c:/docume~1/admini~1/locals~1/temp/tmpb12hgk.nl", line 298, in ?
    if processIsMaster(): file.addToSample(state, 'MPSH 2.0V', label)
MemoryError:
Terminated Abnormally

Can anyone tell me the reason? And how can I solve the problem? Thanks in advance!

13

General Questions and Answers / Re: two "0" values in the calculation result of MPSH energy spectrum. Why?

« on: August 25, 2009, 15:54 »

I see. Thank you very much！

14

General Questions and Answers / Re: two "0" values in the calculation result of MPSH energy spectrum. Why?

« on: August 25, 2009, 15:37 »

Right, no, I don't think there is anything wrong with the script or so. It's just not clear to me exactly how this "0 eV" appears. Is it an eigenvalue of the MPSH spectrum? How does it look, exactly, in the output log?

hi, Blom, I am glad that you give me reply rapidly.
Attached is the result part of the output file.  "0 eV" is an eigenvalue and there are two. Are they all degenerated with fermi level?
thanks

15

General Questions and Answers / Re: two "0" values in the calculation result of MPSH energy spectrum. Why?

« on: August 25, 2009, 13:13 »

Thank you two, zh and Blom.
In fact, I have calculated that system under varied biases, only 0.2V-result has two "0 eV" levels, and the others have no "0" output. I know there may be degenerated levels and they are existent in all my results. Therefore, I think the little problem shouldn't attribute to the script or the configuration. I just can't know the meaning of the two "0" values.