Messages

1

General Questions and Answers / Can van der Waals interaction included in the calculation?

« on: January 11, 2012, 17:50 »

As van der waals force is dominant in layer graphene system? Dose ATK provide any routine to include van der waals interaction in the calculation? How much will the exclusion of van der waals interaction impact the accuracy of the result?

2

General Questions and Answers / Re: A question about three terminal device

« on: October 7, 2011, 14:32 »

Thanks

3

General Questions and Answers / A question about three terminal device

« on: October 7, 2011, 13:01 »

If I construct bulk device with three terminal, like the model in the tutorial" Graphene junction device", which the gate controlling region is finite nanoribbon, so my question is if I construct the three terminal device like the attachment, in the calculation will the gate region be treated also as infinite?

4

General Questions and Answers / Re: Disagreement between the result I got and the result in publication

« on: September 10, 2011, 08:00 »

Another question I think out is that if I have to calculate the electronic structure of Graphene on Boron nitride for example, or Graphene on metal surface, there always seem to be the lattice mismatch, then which lattice constant I should chose? The graphene lattice or boron nitride lattice, since I also want to get the equilibrium distance between two layers……

5

General Questions and Answers / Re: Disagreement between the result I got and the result in publication

« on: September 10, 2011, 06:39 »

Oh, I change the C-C bond and the lattice constant to the experiment value, and this time equilibrium interlayer distance turn out to be around 3.36 Angstrom, Maybe this time it seems right ! Thank you for your help, I did not expect the result relate so closely to lattice constant, sorry for my negligence!

6

General Questions and Answers / Re: Disagreement between the result I got and the result in publication

« on: September 9, 2011, 10:28 »

Howerver, the result I got from serials of calculations for total energy versus interlayer distance also turn out to be around 3.1 Angstrom. It's similar to the result I got from  "OptimizeGeometry()"……

7

General Questions and Answers / Re: Disagreement between the result I got and the result in publication

« on: September 9, 2011, 08:11 »

Actually，the optimized interlayer distance I got using LDA and GGA both are around 3.1 Angstrom……and the paper does not mention the parameter they use… Many other calculation all got the similar optimized interlayer distance of 3.34 Angstrom…So，I found rather puzzled

8

General Questions and Answers / Disagreement between the result I got and the result in publication

« on: September 8, 2011, 12:34 »

Why the optimized interlayer distance of bi-layer Graphene is 3.08 Angstrom, but the value in other publication is around 3.3 Angstrom(reference for http://apl.aip.org/resource/1/applab/v92/i22/p223106_s1 also using ATK), is there anything wrong with my calculation ?

9

Scripts, Tutorials and Applications / Re: Puzzle about the I-V characteristics of bilayer graphene compared with monolayer

« on: September 7, 2011, 09:10 »

Why the optimized interlayer distance of bi-layer Graphene is 3.08 Angstrom, but the value in other papers is around 3.34 Angstrom, is there anything wrong with my calculation ?

10

Scripts, Tutorials and Applications / Re: Puzzle about the I-V characteristics of bilayer graphene compared with monolayer

« on: September 6, 2011, 17:35 »

Generally speaking, is more k-point the better the result? And how to test how much k-point is enough with the combination of accuracy and time-consuming ?

11

Scripts, Tutorials and Applications / Re: Puzzle about the I-V characteristics of bilayer graphene compared with monolayer

« on: September 6, 2011, 09:53 »

Actually, there is something I don't quite understand in your code

Code

    k_min = 0.0
    k_max = 0.02
    k_n = 41

    k = numpy.array([(0,x,0) for x in numpy.linspace(k_min,k_max,k_n)])
    w = numpy.array([ 2 -(numpy.linalg.norm(i) == 0) for i  in k])

the k space you define are from (0,0,0) to (0,0.02,0) ,and what does w mean, I see it define as "kpoints_weights=w", this is what you mean by "user-define k-point around where the band cross the fermi level" ? because in my operation of ATK, I haven't met such settings. Could you explain a bit in detail to me ?

12

Scripts, Tutorials and Applications / Re: Puzzle about the I-V characteristics of bilayer graphene compared with monolayer

« on: September 4, 2011, 12:56 »

Sorry for that！Here are the attachment

13

Scripts, Tutorials and Applications / Re: Puzzle about the I-V characteristics of bilayer graphene compared with monolayer

« on: September 4, 2011, 04:57 »

This is the zero bias transmision spectrum I get from my calculation, actually, I find it hard to understand the transmission spectrum of the bilayer from the band structure.

14

Scripts, Tutorials and Applications / Puzzle about the I-V characteristics of bilayer graphene compared with monolayer

« on: September 3, 2011, 09:13 »

I have done the calculation of bilayer gaphene and monolayer graphene, but I found that the current of bilayer graphene is larger than twice of monolayer graphene when the applied bias is low.(see the attachment)

This is strange because I think in any case the conductivity should be lower than parallel of two monolayer graphene because of interlayer scattering in bilayer system.

So I doubt the accuracy of my calculation, the script is attached, I beg help for checking anything wrong with my setting or is there any question with my assumption for I haven't seen any reference about such phenomenon.

15

General Questions and Answers / Re: A warning about convergence when calculating transport properties

« on: August 9, 2011, 19:36 »

I have calculated the band structure of MoS2 with the unit cell(hexagonal), but the dimension of the unit cell is different from the electrodes in the device model, Can the K-sampling testing from the unit cell apply to the electrodes in the device model?