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Messages - Petr Khomyakov

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1
Did you create your script through the GUI or did some changes in the script itself? It would be helpful to see the actual script, not only the log.

2
Which version of QuantumATK are you using? It would also be helpful to see your python script, log and hdf5 files.

3
To the best of my knowledge, this feature is not available in Band structure analysis object. But typically, getting a band structure requires  a fast, post-processing calculation without a need for SCF calculation. If you want to speed it up, you may always use the KDotPExpansion method available for band structure calculations, see https://docs.quantumatk.com/manual/Types/Bandstructure/Bandstructure.html, which can be set through the GUI as well. That is especially useful feature for hybrid functional band structure calculations. If you need to view only limited number of bands, you may just zoom on the band structure region of interest in the Band structure analyzer.

4
This feature is not implemented in QuantumATK.

5
How do you evaluate that the bond is 1.5? To my understanding, you have got 2 bonds shorter than the 3rd one, kind of consistent with 1 double + 2 single bond picture.

6
You must be able to compute the spin up and down components of the current using the Transmission Spectrum (computed in the study object) as described in the manual, see an example of current calculation at  https://docs.quantumatk.com/manual/Types/TransmissionSpectrum/TransmissionSpectrum.html.

7
I guess you should calculate velocities for any band that crosses the Fermi level, whether one calls it valence or conduction band. For a system with a gap, you would perhaps need to consider the entire DOS, taking a more general definition of capacitance based on DOS as function of energy.


8
EDP*e = -Hartree Difference potential (HDP), which is in units of eV. The plots refer to HDP (eV) as stated in the color bars.


9
Questions and Answers / Re: MoTe2
« on: June 11, 2020, 21:51 »
Also, there is an extensive database for 2D materials at https://cmrdb.fysik.dtu.dk/c2db/.

10
If z-axis is perpendicular to a nanoribbon plane, one should expect no band dispersion, as you say because of weak interaction between neighboring, periodic images of the nanoribbon monolayer.

11
QuantumATK methodology for electronic structure calculations is based on density functional theory (DFT), so there is no many-body wave function, as the method is based on an alternative description of many-body problem, density functional. So, in that sense, one can not do, e.g., restricted Hartree–Fock (RHF) method for open-shell singlets, as it is not implemented  in QuantumATK.

But three-coordinated carbon atoms as such are pretty common to be handled with DFT, e.g., in graphene or carbon nanotube related systems, or benzine molecule or similar. Could you post your python script and related log file for this calculation to see your actual system and settings? 

12
To add on the IV-curve analysis object vs. IVCharacteristics study object, the latter is a study object (not an analysis object), meaning that it allows doing many things that the IV curve analysis object would not, e.g., restarting calculations from the point where it was stopped (if job crashed or stopped intentionally), adding or removing (V_ds, V_gs) points, calculating physical quantities (transmission spectrum, potentials, electron density, density of states and so) directly in the study object, and many other things. 

One thing where the IV curve analysis object might be of use is if for whatever reason one wants to independently set the left and right electrode potentials with respect to a common reference when applying a bias voltage, which is a difference between the left and right potentials. In the  IVCharacteristics study object, the right electrode is grounded, i.e., the potential is set to zero by default (at the moment it is not possible to change this default in the study object settings), and the actual bias voltage is applied by changing the left electrode potential. That makes no difference for devices without gate electrodes, but for devices with gates it is important to be aware of this difference between the IVCurve and IVCharacteristics objects.

13
Regarding computing DOS for graphene see Appendix in Phys. Rev. B 87, 075414 – Published 7 February 2013. As Tue suggested also try increasing the number of k-points significantly. Did you also use tetrahedron method with significantly increased k-point density? It would also be helpful to see your script.

14
This is exactly what my previous post is about that one can define the physical position of the Fermi level when using the Fermi Dirac broadening method available in QuantumATK for DFT calculations for a given electronic temperature, which acts a broadening/smearing parameter in SCF electronic structure calculations, see the manual https://docs.quantumatk.com/manual/Types/FermiDirac/FermiDirac.html for more details.

15
If one uses the Fermi-Dirac smearing (not MP or others) for an SCF calculation, the position of the Fermi level is physical, and one can then see whether a semiconductor is intrinsic or doped by looking at the CBM or VBM position with respect to the Fermi level.

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