Messages

16

General Questions and Answers / Re: IR absorption spectra

« on: October 6, 2020, 10:32 »

Hi,

Yes, the IR spectrum can be calculated using the DielectricTensor object, https://docs.quantumatk.com/manual/Types/DielectricTensor/DielectricTensor.html#infrared-spectrum. The IR spectrum is available in the DielectricTensor analyzer.

You may also find it useful to watch the webinar on simulation of optical properties with QuantumATK:  https://docs.quantumatk.com/webinars/webinars.html#simulation-of-optical-properties-with-quantumatk

Regards,
Troels

17

General Questions and Answers / Re: Negative energy in phonon band structure calculation

« on: September 14, 2020, 16:40 »

Hi,

I noticed that in your geometry optimization, you fixed the strain in the x- and y- directions, while not in the z-direction. I think this is a mistake. For such a 2D material you should rather fix the strain in the z-direction and relax it in the x- and y-directions like:

Code

constraints = [FixStrain(x=False, y=False, z=True)]

Try to re-run the geometry optimization with this constraint and the recalculate the DynamicalMatrix.

Additionally, phonon calculations might require more accurate setting than 'normal' calculations. For this you might consider decreasing the tolerance as:

Code

iteration_control_parameters = IterationControlParameters(
    tolerance=1e-05,
    )

Regards,
Troels

18

General Questions and Answers / Re: Mulliken Poppulation

« on: September 14, 2020, 16:28 »

Hi,

Perhaps you can use the 'bond' method on the MullikenPopulation analysis object, https://docs.quantumatk.com/manual/Types/MullikenPopulation/MullikenPopulation.html#NL.Analysis.MullikenPopulation.MullikenPopulation.bond.

Regards,
Troels

19

General Questions and Answers / Re: Regarding electron exchange and correlation functional in spin transport

« on: September 11, 2020, 12:04 »

Hi,

It's difficult to say which is better. I guess the main difference will be in relaxed geometries. I expect that for similar geometries you will get quite similar results with PBE and RPBE. Personally, I would always use PBE for such a problem.

Regards,
Troels

20

General Questions and Answers / Re: Phonon DOS

« on: September 11, 2020, 12:01 »

Hi,

I don't understand what you need more. Your script seems right, plotting the differently coordinated C atoms in different colors, and there are no errors in the log. So what excactly is the problem?

Regards,
Troels

21

General Questions and Answers / Re: Basis set superposition error correction

« on: September 9, 2020, 09:57 »

Hi,

It is difficult to answer this question very generally. But sometimes basis set superposition errors (BSSE) can be significant leading to an overbinding, i.e. too large binding energy. If you get very different binding energies with and without the Counterpoise correction, it is probably important. In order to address the problem for a particular case, I would suggest that you try to compare your results with plane-wave calculations, using the PlaneWaveCalculator, since this does not suffer from BSSE.

Regards,
Troels

22

General Questions and Answers / Re: Query Regarding high symmetry points in band structure calculation

« on: September 9, 2020, 09:50 »

Why not just leave out one of the points which have the same energy as another high-symmetry point. Did you know, that you can get a visual representation of the high-symmetry points using the Builder->Bulk Tools->Brillouin Zone Viewer.

23

General Questions and Answers / Re: ampacity / current carrying capacity

« on: September 9, 2020, 09:45 »

Hi,

In my understanding, a detailed calculation of the current carrying capacity is an extremely complicated task involving (i) electron-phonon coupling giving rise to current induced heating (i.e. energy transfer from the electrons to the phonon bath and vice versa); (ii) current-induced forces; (iii) this should be coupled with some kind of molecular dynamics simulation to actually model the break-down of the conductor.
Such a full calculation cannot be done with QuantumATK (or with any other tool as far as I am aware).

You can address parts of the problem individually such as electron-phonon coupling or to some extend current-induced forces (calculate the force at finite bias).

Regards,
Troels

24

General Questions and Answers / Re: Geometry Optimization in Germanene Zigzag nanoribbon incorrect results

« on: August 31, 2020, 14:16 »

Hi,

It seems that your unit cell in the C-direction for the ZZNR is too long, since there are no bonds in the C-direction crossing the unit cell edge. I would guess your structure should look more like the attached figure.

Regards,
Troels

25

General Questions and Answers / Re: Query Regarding high symmetry points in band structure calculation

« on: August 31, 2020, 14:08 »

Hi,

You will never create problems in the bandstructure calculation by removing some high-symmetry points. The reason that (Gamma, Z)  and (X, R) have the same energy in your case is probably that you have a vacuum region in the z-direction. In this case, there is no interactions in the z-direction whereby the bands become flat. If this is not the case, then please share your script.

Regards,
Troels

26

General Questions and Answers / Re: 3D band structure plot

« on: August 28, 2020, 14:28 »

Hi,

1) We currently don't have a built-in analysis tool for visualizing 3D bandstructures. However, it is possibly to make your own plot using e.g. the Eigenvalues analysis object, which calculates the energy eigenvalues of a given configuration for a list of k-points. I have attached a script that calculates and plots the valence- and conduction band structure of graphene in a similar way as your attached plot. I hope you can use this as a starting point and modify it for your own applications.

2) We currently don't have an analysis object for calculating projected phonon density of states. However, I have previously shared a script that you can hopefully use. See the attachment here:
https://forum.quantumatk.com/index.php?topic=6427.msg27005#new

Regards,
Troels

27

General Questions and Answers / Re: Phonon DOS

« on: August 27, 2020, 10:42 »

Hi,
We currently don't have an analysis object for calculating projected phonon density of states. However, I have previously shared a script that you can hopefully use. See the attachment here:
https://forum.quantumatk.com/index.php?topic=6427.msg27005#new

Regards,
Troels

28

General Questions and Answers / Re: Query regarding thermoelectric calculation

« on: August 5, 2020, 12:53 »

Hi,
Concerning 1):It sounds like you are doing the right  things. However, it is hard to judge if your results are correct. Can you please share some pictures of the phonon transmissions or hdf5-file with the results. It would also be helpful to compare DFT and FF phonon bandstructures for the electrodes.
Concerning 2): You can add doping to your structure in the Builder ->  Miscellaneous -> Doping.

29

General Questions and Answers / Re: Rashba effect

« on: August 4, 2020, 11:55 »

Hi,

I'm nut sure if I compkletely understand your question, but I would say that the interaction included in QuantumATK will always be between the electron spins and the screened electric field. In addition to this, as you probably know, you can also have Rashba effects from surfaces and interface, i.e. without an external field.

Regards,
Troels

30

General Questions and Answers / Re: projection of phonon band

« on: August 4, 2020, 11:46 »

Hi,

Sure you can project on each atom. I have attached a slightly modified script, which projects on each atom (and plots the contribution from atom 0 and 1 - in this case they are all the same).

Regards,
Troels