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Messages - Petr Khomyakov

Pages: 1 ... 66 67 [68] 69 70 ... 86
1006
General Questions and Answers / Re: Can Work funtion difference between right and left reflect in EDP?
« on: July 7, 2017, 09:55 »
If ATK-2016, then your potentials are defined in new convention that we  will keep for all the future releases, including the newest ATK-2017.0  that is already available for download on our website.   

1007
General Questions and Answers / Re: Can Work funtion difference between right and left reflect in EDP?
« on: July 6, 2017, 19:26 »
What version of ATK are you using? In ATK2016, we had changed definition of the Electrostatic and Hartree Potentials as well as the related Differences. New Hartree potential is (-1) Old Electrostatic potential, and  New Electrostatic potential is (-1) Old Hartree potential. The units of the New Hartree  potential and New Electrostatic potential are eV and Volt, respectively.

1008
General Questions and Answers / Re: armchair mos2 nanoribbon
« on: July 6, 2017, 08:32 »
Take a look at Reply#2 at https://quantumwise.com/forum/index.php?topic=5123.msg22193#msg22193.

1009
General Questions and Answers / Re: Can Work funtion difference between right and left reflect in EDP?
« on: July 6, 2017, 08:23 »
Take a look at the section on "Electron charge density projections" in this tutorial http://docs.quantumwise.com/tutorials/espresso_gui/espresso_gui.html.

1010
General Questions and Answers / Re: silicene armchair nanoribbon
« on: July 5, 2017, 20:47 »
I am not saying that a silicene sheet is not buckled. The question is whether the unsupported narrow ribbon is also buckled; the tutorial does not consider the nanoribbon case, and the forum discussion is not very conclusive on that matter.   

1011
General Questions and Answers / Re: silicene armchair nanoribbon
« on: July 5, 2017, 19:14 »
A silicene sheet or silicene nanoribbon should be buckled? Your system is a narrow ribbon, it is not obvious at all that it is to be buckled as well as an infinite 2D structure.

1012
General Questions and Answers / Re: Tunnelling FET
« on: July 5, 2017, 17:36 »
To emphasize, the WKB approximation-based approach is, in general, also less accurate compared to the NEGF-based approach implemented in the ATK. 

1013
General Questions and Answers / Re: silicene armchair nanoribbon
« on: July 5, 2017, 17:28 »
Maybe the nanoribbon should not be buckled, and the geometry optimizer has actually predicted it. What makes you believe that it must be buckled?

1014
General Questions and Answers / Re: Can Work funtion difference between right and left reflect in EDP?
« on: July 5, 2017, 17:24 »
Quote from: ocdor on July  5, 2017, 10:16
Dear ATK experts,
              I have calculated the EDP(enclosed in attachment). Right and left electrode is 0V,but materials is not in accordence. The work function difference of two electrode materials is 1.1eV. Is my result right?

The difference of the EDP values in the left and right electrodes does not need to be zero if the bias voltage is zero, unless the electrodes are identical and the system has a mirror symmetry, but this is not the case. So, I guess the result is correct.

I would, however, increase the central region of your device, as the electrode extensions now seems to be directly coupled to the overlap region where the actual scattering takes place.

1015
General Questions and Answers / Re: device bandstructure
« on: July 5, 2017, 09:42 »
Strictly-speaking, the band structure is uniquely defined for a perfectly-periodic crystal structure only; this is why there is no band structure analyzer for device configuration.

I guess the band diagram you are referring to is that given by the Hartree Difference Potential (HDP) as discussed in the following tutorial http://docs.quantumwise.com/casestudies/ag_si_interface/ag_si_interface.html. So, you will need to compute the HDP for your device structure, and the HDP curve can then be considered as a visualization for how the conduction (valence) band minimum (maximum) changes across the device.

In the vacuum, the HDP goes to a constant that defines the vacuum level, and you can calculate the Fermi energy with respect to this level.

1016
General Questions and Answers / Re: Tunnelling FET
« on: July 4, 2017, 23:25 »
The ATK transport calculations are not based on the WKB approximation. The ATK solves the scattering problem in an numerically-exact manner, using Green's-function formalism; you may take a look at http://docs.quantumwise.com/manuals/NEGF.html and http://docs.quantumwise.com/tutorials/atk_transport_calculations/atk_transport_calculations.html for more details on the issue.

1017
General Questions and Answers / Re: The problem of device NEGF DFT convergence?
« on: July 4, 2017, 10:45 »
Regarding #2, this is the length of the actual electrode and related electrode extension that need to be enlarged.

Regarding #3, this can be done in the VNL or in the script by replacing 'EquivalentBulk' with 'NeutralAtom' if you saved the script with defaults, or otherwise
explicitly adding the initial_density_type in the Device Algorithm Settings:
#----------------------------------------
# Device Algorithm Settings
#----------------------------------------
initial_density_type = NeutralAtom(
    electrode_constraint_length=10.0*Angstrom,
    )

However, I notice that you may first try changing the electrode length before changing the defaults. There is no guarantee that 'EquivalentBulk' is not a better option compared to 'NeutralAtom'. So, you may want to try both settings if the problem is not gone.

1018
General Questions and Answers / Re: transmission eigenstate
« on: June 30, 2017, 15:39 »
The color scheme is related to the magnitude of the transmission eigenstates defined as described in Notes at http://docs.quantumwise.com/manuals/Types/TransmissionEigenstate/TransmissionEigenstate.html.

1019
General Questions and Answers / Re: Different model between CNT and electrode
« on: June 30, 2017, 15:19 »
There is no short answer to your question. There is a plenty of experimental and theoretical literature on this topic, so I would suggest researching this in google scholar or web of science. For example, there is this paper on the metal-nanotube contact at http://aip.scitation.org.proxy.findit.dtu.dk/doi/abs/10.1063/1.2405393.

1020
General Questions and Answers / Re: MoS2
« on: June 30, 2017, 15:10 »
It really depends on what you want to simulate by doing these calculations. Nanoribbons are usually placed on a substrate that may constrain the nanoribbon structure in some way. It can also be an unsupported or partly supported nanoribbon. You would perhaps need to make the choice yourself, based on your research goals and scientific intuition.

The tutorial with an example of how to do geometry optimization is mentioned in one of the previous posts.

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