Messages

1

General Questions and Answers / Re: a question about temperature in two probe calculation

« on: August 8, 2009, 10:58 »

Dear zh
Thank you very much, now I know how to do.
Best regards.

2

General Questions and Answers / Re: a question about temperature in two probe calculation

« on: August 8, 2009, 04:26 »

Dear Anders Blom:
    Thank you very much!
    I understand what you said, according to your explanation, I think my results are obtained under 300K (room temperature). So the referee may be ask  another question. As we all know, as  the temperature is 300K, the interaction between electrons and phonons should be considered, and he will ank me whether the interaction is considered or not, according to your explanation, the temperature has nothing to do with phonons. So I think he will not believe what I said. How to further explanation this question? If my results are abtained under 0K, or around 0K, Is the answer which the referee really want? I really get confused. By the way, I read a lot of papers, and the papers are not referred to the temperature, so l think it is a difficult question to answer.

3

General Questions and Answers / Re: a question about temperature in two probe calculation

« on: August 7, 2009, 14:21 »

Dear Anders Blom:
    Thank you very much!
    But I am still confused according to Nordland's explanation. The follows are his explanation:"
The temperature in ATK is only used for determining the shape of the fermi distribution,
and hence it is only used for calculating the density matrix and for evaluating the current.
The manual explains that the user should not think of this temperature as an experimental, physical temperature.
The two-probe calculation is using the temperature defined in the electrodes, but only for smearing of the fermi distribution.
If you force me to say what temperature ( as I would rather not bring physical temperature into the picture)  the two-probe calculation is done
under, I would say it was zero temperature, but the electrons feels a finite temperature"
and accordong to his explanation, I think it was zero temperature, but I am still not sure. By the way, the principle of calculation transport property for the two probe system is basisd on the Green's function, according to my knowledge, the Green's function works around 0K. I don not sure whether I have understood or not, Please give me a detail explanation.Thank you!

4

General Questions and Answers / a question about temperature in two probe calculation

« on: August 7, 2009, 13:31 »

Dear Nordland and everyone:
I have a question about temperature in two probe calculation, I calculate the transport energy spectrum of two probe graphene system by using theATK, and I have written a paper and submitted to APL, I received the reviewer comments today. One quesiton which I do not know how to answer, the quesiton is "The temperature at which the transmission probability and I-V curves are obtained is not stated". I do not know how to answer? what is the temperture for two-probe in ATK? is it 0K, 300K or other? 300K is a default value for two leads when I calculate the transport property of two probe system.
Thank you for your attention!!!

5

General Questions and Answers / Re: How to build two probe system based on graphene ribbon of deformation ?

« on: June 30, 2009, 03:51 »

Dear Anders Blom:
    Thank you very much! I will try.

6

General Questions and Answers / Re: How to build two probe system based on graphene ribbon of deformation ?

« on: June 26, 2009, 16:11 »

Dear Anders Blom:
    Thank you very much for your answer!
  On the one hand, I want to build two probe system based on graphene ribbon of deformations uniform. Just as your said,  the deformations can be considered to a stretch of the ribbon in some direction. For example, if I strech the zigzag  (armchair) ribbon along the zigzag direction or armchair direction, there are two kinds of C-C bond which the changed length will be different, and the corresponding C-C bond angles also be changed. How to obtain the script?
  On the other hand, if the deformatioms are not uniform. Howerer, the deformations are uniform along zigzag or armchair direction. For example, if I stretch the central ribbon along Z direction, the C-C bonds of changed length become  larger and larger from central region of the ribbon to edges. How to write the scipt and connect the two electrodes (I think the electrode also need to chang in order to connect the deformations of central ribbos)?     
    Thanks again, Anders Blom. My English is poor, I think whether you can understand the meaning of above or not.

7

General Questions and Answers / How to build two probe system based on graphene ribbon of deformation ?

« on: June 26, 2009, 10:03 »

Hello, everyone!
I want to anwser a question about graphene ribbons,  I expect to build two probe system based on graphene ribbons of deformation. More specially, if I know the change of  the C-C bonds and C-C angles, when I drag the graphene script into molecular builder or atomic manipulator, I can not chang the C-C length and C-C angles. Can someone offer some script for this?
Thank you very much!

8

General Questions and Answers / Re: How to calculate the density of states (DOS) of isolated region in graphene?

« on: May 30, 2009, 05:55 »

To Anders Blom:
     Thank you very much! I will try to use the functionality in ATK.
     
     

9

General Questions and Answers / Re: How to calculate the density of states (DOS) of isolated region in graphene?

« on: May 29, 2009, 15:00 »

To Anders Blom:
    Thank you very much! According to your explanation, it means that  "scattering region DOS" just a broadened energy level. Therefor, if I want to calculate the  "scattering region DOS" , I only need drag the molecular( "scattering region" ) into VNL, then calculation its "Molecular energy spectrum". Is it right?  By the way, a similar problem which I have met, figure.2 showed the transmission a isolated CNT in the paper (CHIN.PHYS.LETT,Vol.25,No.9,3213(2008)), I do not know how to get this transmission of a isolated CNT by using VNL, since there are not transmission option when I just drag the scattering region molecular into VNL. I guess whether this result is obtained by the other soft or obtained by ATK script or not.
    Thanks again! ANders Blom.
    In addition, a question about bilayer graphene, if you have finished the design, please upload it, I want to design the bilayer graphene model according to your explanation.

10

General Questions and Answers / Re: How to set up bilayer graphene model?

« on: May 28, 2009, 11:40 »

To Anders Blom:
    Thank you very much for your answer, I will try according to your said. I consider ribbons, and I have download a script from graphen tutorial. The scipt is very convenient to set up the graphene ribbons models, and it is just need to modify the parameters of the width and repetitions. Do you investigate the graphene by using ATK?

11

General Questions and Answers / Re: How to calculate the density of states (DOS) of isolated region in graphene?

« on: May 28, 2009, 11:32 »

To Anders Blom
    Thank you very much for your answer! It is just like you said, I also think only the infinite system or periods systm have DOS. I got confused after I read a paper about grpahene (APL94-173110), if you have time, please read it,  and if you can not get this paper, I can sent it to you, please tell me your E-mail or QQ. There is a picture in this paper (Fig2(a)), I am sorry that  I do not know how to upload this picture.
Thank you again, Anders Blom.

12

General Questions and Answers / How to calculate the density of states (DOS) of isolated region in graphene?

« on: May 28, 2009, 10:08 »

Hello
Everyone!
    I have a question about graphen, the two probe system is made of two electrodes and central molecule. The calculation of two probe system's DOS is very easy by using ATK. Howerer, I have read a lot of papers about calculation of DOS in isolated region, this is to say, no consider of two electrodes' affect. But I met a problem when I want to calculate the DOS of isolated region, when I drag the central molecule into VNL, I find that there is no DOS option in VNL, so, I want to know how to deal with this problem by using ATK?
Thanks!

13

General Questions and Answers / How to set up bilayer graphene model?

« on: May 28, 2009, 09:53 »

Hello, everyone!
    I want to set up bialyer graphene model, how to set up the model? my electrodes and the central region are the same materials (bilayer graphen)?
    Thank you very much!

14

General Questions and Answers / Re: How to set up the parameters to "Geometric Constraints" in VNL?

« on: May 26, 2009, 04:21 »

To Anders Blom:
    Thank you very much! So if I want to fix atoms in the central region, I need to know the ordinal number of atoms. By the way, the ordinal number of atoms are seperated by comma. For example, I want to fix the number of atoms (40,41,42,43,44,45), so I need to write 40,41,42,43,44,45 in "Geometric constraints". Is it right?

15

General Questions and Answers / How to set up the parameters to "Geometric Constraints" in VNL?

« on: May 25, 2009, 15:19 »

Hello
   I have met a question  about VNL, when I drag the two probe system into VNL. First, I want to optimize the geometric, but I do not konw how to set up the parameters in "Geometric constraints"? According to the VNL books, "geometric constraints" is a list of atom indices whose positions should be fixed during the optimiaztion, and the indices are integers ranging from 0 to N-1, where N is the total numbers of atoms in the atomic configuration.
  So I have two questions:
   First, Does N include the two electrode atoms?
   Second, if I have 200 atoms in the central region, and 50 atoms in the two electrode atoms, the total atoms is 250.When I fixed the electrode atoms, only optimize the central atoms,  what I need to write in "Geometric Constraints" ?
Thank you very much!