Messages

1

General Questions and Answers / Re: I-V curves for 2D materials

« on: April 4, 2017, 21:23 »

Thanks a lot, Anders. I will check whether the density has a effect on the I-V characteristic.

2

General Questions and Answers / Re: I-V curves for 2D materials

« on: April 4, 2017, 21:06 »

Yes, from the DOS, I think my calculation result is right, because I get the similar DOS as in the reference, a minor modification around -2 eV. And for the transport calculation, my simulation is also along the armchair direction, there is barely difference for the I-V curve (as attached), while a obvious effect for adsorption in the reference.

So, I am really confused. Is it because we are studying a totally different molecule or something is go wrong with our simulation?

3

General Questions and Answers / Re: I-V curves for 2D materials

« on: April 4, 2017, 20:47 »

If you make the system 2x larger in the periodic direction and add one more molecule, that's the same density. So I'm just saying you need to add more molecules in the same system, without making it larger, if you want a bigger effect.

And one more question, back to the answer of Petr, if the molecule does not affect the DOS near the Fermi level, we do not expect a large change in the I-V curve, right? But for the example I mentioned above, NH3 only has minor modification around -2 eV and still the calculation results demonstrate a obvious change in the I-V curve before and after the adsorption.

Thank you.

4

General Questions and Answers / Re: I-V curves for 2D materials

« on: April 4, 2017, 20:42 »

Thanks. That is what exactly I mean.

5

General Questions and Answers / Re: I-V curves for 2D materials

« on: April 4, 2017, 20:04 »

Sure, try that Just add more molecules, but in case you do so and at the same time make the cell larger in the periodic direction, then nothing changes.

Sorry, I don't quite understand. Do you mean nothing will change if we increase the density, here the density I mean, is to increase the number of molecules on the surface of same area rather than repeat the supercell along one direction.

Thanks.

6

General Questions and Answers / Re: I-V curves for 2D materials

« on: April 4, 2017, 17:54 »

Thanks a lot, Petr and Anders.

Yes, the central region includes the left and right electrode extensions, and also another concept is the screening length.

I got to know the VNL-ATK uses the ballistic approximation to do the transport calculation, so the length along the transport direction does not affect so much to the computational workload. I simply want to compare the I-V curves, specifically the different responses for current before and after the adsorption. As you can seen in Figure 4 the paper above, there is a discrepancy (although it might not be large) for the current values after the adsorption of NH3, but barely no difference observed in my simulation results.

Based on your answer, my setup for the simulation seems okay, and in this way, I wonder if I could enlarge the differences, i.e., increase the molecule density in the transport direction (Z) or periodic direction (B) (suppose A is the vacuum)? Because in the experiment, there is a large reduction in the resistance, for this particular molecule is more than 50% reduction.

7

General Questions and Answers / Re: I-V curves for 2D materials

« on: April 4, 2017, 16:09 »

Thanks a lot, Petr.

1. I checked your previous post on the perfect, infinite system, I guess there is no problem if we calculate the transmission and I-V curve under zero bias rather than a finite bias. In my case, do I need to change the BP electrodes to metallic electrodes?

2. The adsorption configuration is the most stable configuration determined by DFT calculations, and indeed, there is no obvious modification to the DOS near the Fermi level. In the previous theoretical calculation about phosphorene, https://arxiv.org/ftp/arxiv/papers/1406/1406.2670.pdf, the NH3 molecule does not affect the substrate (only some minor modification on energy around -2 eV) but still a large reduction in the current values. In their simulation, the scattering region is even smaller and the density of molecules is higher than my simulation, and this cannot be achieved in VNL-ATK, because the length of electrode region cannot surpass that of scattering region. They used TranSiesta package instead.

I want to compare the resistance or conductance of the system before and after the adsorption (under zero bias), to illustrate the sensitivity of the substrate. So, if there any methods that I can do to increase the discrepancies for I-V curve before and after adsorption, such as change to a metallic electrodes, increase the density of molecules, or I just can't?

Thanks for your help.

8

General Questions and Answers / I-V curves for 2D materials

« on: April 2, 2017, 21:44 »

Hi,

I am currently doing some benchmarks for the adsorption behavior of 2D materials. According to the experiment and previous theoretical calculations, normally there is a increased resistance (or reduced current values) after the adsorption of gas molecules on the surface of 2D materials.

But for my results, there is barely a difference before and after the adsorption. Could anyone please tell what is possibly going wrong?

Thanks a lot.