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Messages - Petr Khomyakov

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It is required to accurately compute the Fermi energy in the electrodes. It is impossible to say exactly how many points you need, as it is a matter of convergence tests. Typically, if you have convergence issues with SCF device calculation, one of the possible reasons for that is inaccurately-computed Fermi level. In general, one should also converge the k-point sampling in the lateral directions as well - for CNT, that would just mean that you should have sufficiently thick vacuum padding around the tube to avoid spurious interaction between periodic images of CNT.

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For license issues, please send your request to quantumatk-support@synopsys.com.

33
Please upload log files related to the calculations as well.  Note that 2016.4 is no longer supported version.

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Questions and Answers / Re: SET
« on: July 10, 2019, 15:16 »
There is no standard feature of doing it for a single-electron transistor, as QuantumATK considers the electron transport in the coherent regime, dealing with single electron wave functions, not with sequential tunneling. I think you should first decide on the model you want to use for SET, and then see if the parameters of that model can be computed in QuantumATK in one way or the other.

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It is hard to say anything without seeing your scripts and logs, and knowing what exactly you have done to get those IV objects. What version of QuantumATK are you using?

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Your issue might be related to a bug in computing transmission from bulk configuration calculations. We are currently investigating this. I suggest doing transmission calculations using device configuration (even for perfect bulk material) to avoid any issues. 

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Which version of QuantumATK are you using?

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Yes, that is correct.

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Transmission coefficient is unitless physical quantity, and it is computed per lateral unit cell of the scattering region, i.e., if you, for instance, double the lateral unit cell size in your transport calculations, the transmission will then increase by factor of 2. 

In the Landauer-Buttiker formalism for the electron transport, total transmission can also be seen as conductance in units of G_0, https://en.wikipedia.org/wiki/Conductance_quantum.       

DOS is given in # of states per eV (per unit cell, not unit cell area). Integration of DOS  x Fermi-Dirac distribution (at a given temperature and Fermi energy) over the  energy should  give you the number of electrons (per unit cell) in the system.   

40
Questions and Answers / Re: electrode not perfect
« on: July 9, 2019, 09:40 »
That is totally up to you how to build it. I believe there is no way of making perfect periodic cone without breaking it - this is what QATK did for you. If you want a smooth transition between the scattering/central region and the electrodes, you have to decide on what kind of electrodes you want to attach to the central region. 

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Questions and Answers / Re: electrode not perfect
« on: July 8, 2019, 21:48 »
Perfect electrode means periodic electrode, so that you will have to attach a semiinfinite periodic structure to your carbon cones on the left and right side of the point contact to be able to build a device configuration. 

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The oldest version that is currently available for download at https://solvnet.synopsys.com/ is 2017.12. Unfortunately, version 2016.4 is no longer distributed. You may request a free trial version of recent QuantumATK 2019.03-SP1 at https://www.synopsys.com/silicon/quantumatk.html.

43
Questions and Answers / Re: i have a question
« on: July 3, 2019, 10:32 »
The mobility is actually computed as a tensor quantity, i.e., accounting for crystal structure anisotropy, see the manual and usage example at https://docs.quantumatk.com/manual/Types/Mobility/Mobility.html.

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Unfortunately, we do not support 2016.4 version any longer. This functionality is available in newer versions. Please consider upgrading to a recent QuantumATK version at https://www.synopsys.com/silicon/quantumatk.html, where you can apply for a free trial version.

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But we calculated without inclusion of ghost atoms.We took difference between this Hartree difference potential and Chemical potential which is the work function and obtained 5.24 eV for ZGNR.But the maximum reported value in litreature for graphene is 4.9 eV.

I am not sure I understand your argument regarding "maximum reported value".  Moreover, comparing work function of pristine graphene sheet with that of a narrow graphene nanoribbon (with or without functionalization) does not make much sense, at least to me.

How and where to include the ghost atoms???
What should be the maximum vacuum padding to be fixed???
What boundary conditions to be employed for this kind of structure???

I guess one would have to do actual calculations to answer all these questions. To avoid using ghost atoms, which is very tricky within the LCAO approach for such open structures as yours (compared to closed-packed structures such as Ag metal used in the work function tutorial), one could try using plane-wave basis set to do these calculations. The plane-wave approach is available in recent versions of QuantumATK.

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