Messages

31

General Questions and Answers / Re: Query Regarding photocurrent in Silicon p-n junction

« on: August 3, 2020, 11:20 »

Yes, the picture is somewhat misleading.
The doping is applied to the left and right electrode respectively as written in the tutorial text.
Please also refer to the script silicon_pn_junction.py attached on the tutorial.
There doping is clearly applied to the left and right electrode regions.

32

General Questions and Answers / Re: MoTe2

« on: August 3, 2020, 11:11 »

It is hard to say if the structure is correct or wrong from the picture.
Most likely you do not use enough k-points so make sure that:
1) You use enough k-points on the calculator (for example a 2D sampling of 51x51 k-points depending on the 2D material. In general, do a convergence test to check it).
2) You should use a much denser sampling in the bandstructure (100 points per segment or similar) as you want to probe what happens near the fermi-level.

Also notice that the TMDs come in two structures. A metallic and a semiconducting one.

33

General Questions and Answers / Re: optical spectrum

« on: August 3, 2020, 10:00 »

Hi,
While it is not an option in the gui, the query functions do have a spin-input variable.
For instance you can call "absorption_up = optical_spectrum.absorption(spin=Spin.Up)".
Please refer to the reference manual entry for OpticalSpectrum for other query function examples.

34

General Questions and Answers / Re: Mobility calculation on graphene

« on: July 10, 2020, 15:10 »

I can reproduce the error.
It seems like the plotter fails for samplings with 1 q-point in the tetrahedron method.
For now I think the best option is to artificially set the number of q-points to 2 if the tetrahedron method is needed or use the gaussian method for 2D systems.
It is also possible to access the data directly through query-functions on the object.
Thanks for posting the issue, this is a new bug in 2019.12.sp1 and we are investigating the origin.

35

General Questions and Answers / Re: Mobility calculation on graphene

« on: June 25, 2020, 10:49 »

@paramjot:
It seems from your example that you only include 1 k and q point? Do I understand correctly that you try to do a calculation not for the primitive cell but a large graphene unitcell?
Parallelization will only help if you have k and q points.

@Roc2019:
Yes, it will work for polarized calculations. You can also do the spin life-time (check the ElectronPhononCoupling object description in the reference manual if interested).

36

General Questions and Answers / Re: Mobility calculation on graphene

« on: June 23, 2020, 09:43 »

Hi,
So guess you are following this recently updated tutorial:
https://docs.quantumatk.com/tutorials/mobility/mobility.html

The time-limiting step is the full (k,q)-dependent electron-phonon coupling (EPC). If this is not the case then please state where you are waiting.
It should take approximately 10 hours on a 16-core node to do the EPC in the tutorial.
If that is not the case then maybe check again that all the settings are as in the tutorial.

In general, the EPC can be parallelized over many processes (as there are many combinations of k and q-points).
The following Mobility calculations can be done on a single core and only takes a few minutes.

37

General Questions and Answers / Re: Error during phonon calculation

« on: June 23, 2020, 09:32 »

Hi,
This sounds like you don't have enough available memory.
Your possible ways forward:
1) To reduce memory consumption try to set the number of repetitions manually.
That is replace
repetitions=Automatic,
with
repetitions=[3,3,1] for instance. Check that the dispersion looks correct. One should converge with the number of repetitions.
2) Change LCAO basis set to a less memory consuming one. Usually FHI uses less memory than the default PseudoDOJO. But the accuracy might also be lower for some systems.
3) Allocate more memory per process on the server.

38

General Questions and Answers / Re: Tag option for optical properties

« on: June 17, 2020, 10:15 »

Hi,
I am not certain what exactly you would like to get so maybe say a bit more if you would like more specific help. If the extra layer modifies the states in the first but is not optically active it should come out like that.
We do not have a tag option for optical properties but we have recently made the optical transition matrix elements into a LowLevelEntity (so it is accessible to users directly).
You might be able to take the elements and do the manipulations you need.
There are functions calculateMomentumMatrixElements and calculateDipoleTransitionMatrixElements that can be imported like this
from NL.Calculators.LowLevelEntities import calculateDipoleTransitionMatrixElements
The function takes: p= calculateDipoleTransitionMatrixElements(configuration, kpoint, number_of_states)
where p is a 3 x number_of_states x number_of_states matrix (includes states up to the specified number).

39

General Questions and Answers / Re: superconducting transition temperature

« on: June 17, 2020, 09:34 »

Hi,
QuantumATK does not currently have a finalized feature for the superconducting transition temperature.
It could be done in script as all the ingredients are present, e.g. the electron-phonon coupling matrix elements needed for the Eliashberg function.
It will most likely be a feature in the future but when will depend on the number of requests.

40

News and Announcements / Re: Fermi velocity

« on: June 15, 2020, 10:02 »

Hi,
There is a FermiSurface analysis object:
https://docs.quantumatk.com/manual/Types/FermiSurface/FermiSurface.html

When opening the result in the Viewer analyzer in nanolab then open the "Fermi Surface" menu.
This will allow you to tick on "color by gradient" and choose a suitable colormap.
An example for Ruthenium of Fermi-surfaces and the contribution from individual bands can be seen here:
https://arxiv.org/abs/2001.02216

41

General Questions and Answers / Re: Mismatch of bandstructure and density of states

« on: May 22, 2020, 09:01 »

Hi, If you increase the k-point sampling (in the 2D periodic directions) they will correspond to each other.
You can try to compare the DOS spectra obtained with either gaussians or the tetrahedron methods as described in the example in the reference manual:
https://docs.quantumatk.com/manual/Types/DensityOfStates/DensityOfStates.html

Alternatively it could be that your k-point route used in the bandstructure does not contain the point where the minimal gap is located. The DOS integrate over all k-points in the Brillouin zone.

42

General Questions and Answers / Re: Calculate mobility or conductivity of 3-D bulk material

« on: May 11, 2020, 12:13 »

Hi,
Yes, quantumatk mobility analysis can be done for 3d-materials.
We have published examples for
Systems of different dimensions (see fig. 8, incl. Silicon): https://arxiv.org/abs/1701.02883
A selection of bulk metals: https://arxiv.org/abs/1905.02794 and https://arxiv.org/abs/2001.02216

Calculations for 3D systems are more heavy than 2D and 1D systems.
For large disordered systems, such as amorphous structures, you could consider the special thermal displacement method instead: https://arxiv.org/abs/1706.09290
However, the mobility object offers more analysis options (contributions from individual modes for instance).

The precision of the simulations are equivalent to that of DFT. If the material of interest is accurately described by DFT (correct phonons and band structures) then you can expect the mobility to compare well to experiments probing the phonon-limited mobility.
If the experimental value extracted is limited by other processes (impurities or similar) you would need to perform a model for that scattering rate.
The mobility object allows you to include a user-given scattering rate on top of the electron-phonon coupling rate calculated by QuantumATK.

43

General Questions and Answers / Re: Query regarding deformation potential constant

« on: April 20, 2020, 11:10 »

There is an analysis object for Deformation Potentials:
https://docs.quantumatk.com/manual/Types/DeformationPotential/DeformationPotential.html#deformationpotential-c
This analysis object will assist in fitting a linear or constant deformation potential to the full electron-phonon coupling.

44

General Questions and Answers / Re: Optical transition matrix element

« on: January 13, 2020, 15:42 »

QuantumATK can calculate the optical transition elements (elements of the momentum operator) and several optical properties derived from those.
Currently the matrix elements are not directly exposed but the analysis objects using them are, which might be what you need.
See for instance OpticalSpectrum for Bulk configurations:
https://docs.quantumatk.com/manual/Types/OpticalSpectrum/OpticalSpectrum.html#opticalspectrum-c
Or the PhotoCurrent object for devices.

45

General Questions and Answers / Re: photocurrent

« on: June 4, 2019, 10:53 »

Convergence checks should be performed for the usual DFT settings.
When a good DFT simulation has been performed the kpoints and energies/energy_resolution used in the Photocurrent calculation should be checked.

A bias voltage is included in the usual way through the device calculator. Then one perform the calculation of the Photocurrent for each separate and converged device configuration at a given bias voltage.

The Photocurrent object has a query function "photocurrent.photonMediatedTransmission(photon_mode,...)" that can be used to obtain the transmissions as a function of energy for a selected photon energy index "photon_mode".
Please see the reference manual entry for Photocurrent for full description of the inputs to this query function:
https://docs.quantumwise.com/manual/Types/Photocurrent/Photocurrent.html#photocurrent-c