[Smeagol-discuss] How to avoid the noise in the Transmission?

[Wang Qinjing]

Hi Salvador:

The TRC curve I show is for zero bias calculation, in which I didn't get the message "no. of left channels .ne. number of right channels".

Cheers 

Yours Wang
  ----- Original Message ----- 
  From: Barraza-lopez, Salvador 
  To: Wang Qinjing 
  Cc: smeagol-discuss at lists.tchpc.tcd.ie 
  Sent: Friday, February 27, 2009 1:33 AM
  Subject: Re: [Smeagol-discuss] How to avoid the noise in the Transmission?



   Hi Wang,

   The TRC curve you show is for zero bias or nonzero bias? I'd encourage you to see if, for that particular run, you get the messages. If you don't get them there, the problem lies elsewhere.

    If your geometry has vacuum in the x-y directions you'll have no dispersion and there is no use in doing the k-point run.

   On point 3, you've got the idea, if you change your energy sampling by increasing, say by 1.5 the number of energy points (or other clever way to "miss" the two energies where you have problems) you may get rid of the feature that way.

  -Salvador.


  ----- Original Message -----
  From: "Wang Qinjing" <041019019 at fudan.edu.cn>
  To: "Salvador Barraza-lopez" <sbl3 at mail.gatech.edu>
  Cc: smeagol-discuss at lists.tchpc.tcd.ie
  Sent: Thursday, February 26, 2009 12:03:40 PM GMT -05:00 US/Canada Eastern
  Subject: Re: [Smeagol-discuss] How to avoid the noise in the Transmission?

   
  Salvador:

  Thank you for your suggestions.

  As you guessed, I often see the message:
  " no. of left channels .ne. number of right channels "

  But I often get this message when bias is applied. However, these depressions exist in zero-bias system.

  I have tried some as you suggested

  (1) Increasing the parameter Delta:
  I've increased Delta from 1.d-6 to 1.d-4 or even higher, namely 1.d-1, the TRC doesn't change. The depressions still exist.

  (2) K points
  Yes, I really do the calculation with Gamma point only. I will try your suggestion to increase the number of k points. 
  However, both my lead and scattering region have vacuum at both x and y axis. For this reason I think Gamma point only is 
  enough. I will post my result with increased k points later.

  (3) changing the number of energy points.
  Do you mean to avoid the energy point at which the singularity problem exists? I believe in that way the depressions will be
  removed.

  Thank you.

  Yours Wang


    ----- Original Message ----- 
    From: Barraza-lopez, Salvador 
    To: Wang Qinjing 
    Cc: smeagol-discuss at lists.tchpc.tcd.ie 
    Sent: Thursday, February 26, 2009 11:13 PM
    Subject: Re: [Smeagol-discuss] How to avoid the noise in the Transmission?


     Some times during calculation of transmission coefficients you get the following message:
    no. of left channels .ne. number of right channels

    Look at your output and seek any warning message like the one just mentioned.

    If you are indeed getting a couple of these messages, the associated transmission at these energy points is skipped; it will not be written to file. You'll miss it on the TRC file. It means there's some singularity 
    at those energies and the self-energies are not computed. If they are skipped in the file it'll appear as a depression at isolated points on the TRC plot.

    Suggestions, in case you do see the warning message I mention (or other similar) in your output.

    (1) Try increasing your Delta parameter, say by one order of magnitude or so. This will perhaps help avoiding singularities on the construction of the self energies for transmission purposes.

    (2) Is you calculation with Gamma point only? If so, you could increase the number of k-points; that'll average the noise out.

    (3) Other thing I'd suggest is changing the number of energy points in your TRC file. You may very probably miss these points (and get other similar ones in other energy regions probably).

     Cheers,
    -Salvador.


    ----- Original Message -----
    From: "Wang Qinjing" <041019019 at fudan.edu.cn>
    To: smeagol-discuss at lists.tchpc.tcd.ie
    Sent: Thursday, February 26, 2009 3:47:51 AM GMT -05:00 US/Canada Eastern
    Subject: [Smeagol-discuss] How to avoid the noise in the Transmission?


    Dear all:

    I've sent this email before, unfortunately it is hold because the the attched file is over the limit of 40 KB. I resend the email now:


    Dear SMEAGOL users:

    I am calculating the transmission of a lead-molecular-lead system by SMEAGOL and get the relation of the transmission coefficient and the energy from the output file *.TRC. The picture of TRC versus energy is also sent as attachment.

    My problem is, are the two peaks at about -0.12 Ry and -0.15 Ry, as pointed out by two red arrows, the noise in the transmission? It seems there are not any physical meanings. Are they really noise? If they are noise, how can I avoid them?

    Thank you all in advance

    Wang Qinjing

    =====================================
    王秦镜 复旦大学物理系研究生
    Wang Qinjing, Postgraduated students
    Physics Department, Fudan University
    =====================================

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