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This also means that the position and geometry of the gate is just as important as the gate voltage. The closer the gate is to the atoms, the bigger effect it has.Thanks for your reply. I use the ATK 2008.10. There is only the paramater that the atom number applied of voltage gate. How to understand "The closer the gate is to the atoms, the bigger effect it has"
This also means that the position and geometry of the gate is just as important as the gate voltage. The closer the gate is to the atoms, the bigger effect it has.Thanks a lot for your reply. I use the ATK 2008.10. I applied the gate voltage on the first molecule and the second molecule of the scattering region, respectively. I just study the effect of gate voltage applied different positions on the electronic propersities of the molecular device. I want to know how the 'gate' voltages translate into orbital energies. Did the ATK 2008.10 apply the gate voltage uniformly to the atoms of the molecule? If this is the case then the result is not physical, since each gate will contribute to the energy shift on all atoms nearly identically (since the capacitance between each gate and
The above is correct, but it also depends on how the "gate" was applied. An alternative way to apply it (indicated perhaps by your notion that it's only applied to part of the system) is to introduce a shift of the onsite energies (the old "gated method" in ATK 2008.10 and earlier, and also still possible in 12.2 and later, but with another method). In this latter case I would tend to agree with the reviewer that it's unrealistic to assume that some atoms in a very small region are "gated" and other ones not - if, that is, you really mean this to simulate an external gate. There is also internal gate effects, more properly I guess charging effects which can be caused by reduction/oxidation of individual atoms or side groups. This charging effect can be simulated using an onsite shift to some extent (and in the upcoming ATK 13.8 but a real localized charge on an atom). Ultimately, you have to be able to argue your case why you have simulated the system in a particular way and what physical relevance it has, otherwise the study has no meaning.
I think you have made a very interesting study, and clearly shown how the gate voltage actually tunes the electron charge in the central region, by adding and removing charge. Sure, a positive value would mean charge is moved from the electrode to the central region (the part you use to sum up the charge), which is allowed since the system is in non-equillibrium and we have non-conservation of charge.In the question about the transfer charge above, i find the gate voltages choosed in his model is very big, and can you tell me whether enough surface layers are need?
To relate the conductance to the charge, you probably have to analyze the transmission spectrum, and perhaps also the molecular levels, and see how these change with the gate. They probably move, and that's why the conductance changes. Depending on the nature of these levels, etc, you can analyze the system further. There is no simple way to say whether adding or removing electrons will decrease or increase the current/conductance, it depends on the details, but basically this is the working principle of a transistor, where the primary current (source drain) is controlled by a much smaller current (the gate).
Based on this, and other things too perhaps, you can hopefully draw your conclusions and publish a nice paper
You may want to have a look at how other people analyze systems with a gate voltage, and compute various quantities. Search for "transistor" on the publication page and see e.g. the two graphene articles from 2007.
Thanks for your help!Can you tell me how many surface layer in your model? I find the gate voltage in your mode is very big and whether the enough surface layers are needed? Thanks.
I have already analyzed the transmission spectrum and the molecular levels, and just have some puzzle in the change of the transfer charge.
After reading you answer, i have understood it. Thanks again!
You mean you specifically want to study the effect of the molecules in neighbor cells interacting? It's hard to say which precise model you need, probably you need 5x5 also at least, because you need to get into the situation when there are no interactions, in order to say which effect comes form the interaction itself.I calculate the IV properties of the models Ag(3*3)-C60-Ag(3*3) and Ag(4*4)-C60-Ag(4*4) and . Negative differential resistance （NDR） in the current-voltage curve can be observed for former but cannot be observed for the later. I want to know the reason that causes the different electronic transport behaviors.
The electrode setup in the electrode region is not reasonable. Its unit cell size in the xy plane must be larger than the cross section of CNT in the center region.If the CNT in the center region forms bond with the CNT in the repeater xy plane, can the electronic transport properties be calculated with ATK? Thanks.
That difference will be because of molecule interactions.Dealing with the question of the effect of molecule interactions, is it reasonable to use the models Ag(3*3)-C60-Ag(3*3) and Ag(4*4)-C60-Ag(4*4)?
When discussing "accuracy", the question is always "Compared to what?" If you experiment (envisioned or real) deals with a single molecule, then you had better simulate a single molecule, without bonds to (artificially) repeated copies. On the other hand, in many real experiments, the molecules on a metal surface can be placed rather densely.In the model Ag(3*3)-C60-Ag(3*3) and Ag(4*4)-C60-Ag(4*4), we observed the C60 forms bonds with repeated copies in the former model but cannot be observed for the later model. Also i find that they show the different IV characteristics obviously. Iwant to know if they can be viewed as the effect of size of electrodes on the electronic transport properties or the effect of interaction between the C60 moleculers on the electronic transport properties. Thanks.
Generally, however, you had better avoid direct formation of bonds (more specifically, basis set overlaps).
