Messages

16

General Questions and Answers / Re: missing parameter set for force field calculations

« on: July 30, 2019, 08:48 »

Dear tada,

you might want to search the literature for force-fields including parameters for all the species you are interested in.

If these are available, you can add them to the force field, or even create a custom force field from scratch, by using the TremoloX potential editor.

Best regards,
Daniele

17

General Questions and Answers / Re: The problem of setting of ferromagnetic and antiferromagnetic states

« on: May 20, 2019, 09:16 »

Dear Bertha_He,

in order to set the FM solution, you should set the spin of the Mo and S atoms to spin = +1, whereas for the AFM solution, you should set the Mo atoms to a spin = +1 and the S atoms to spin = -1. It might be also useful to set the keyword fixed_spin_moment (see e.g. https://docs.quantumatk.com/manual/Types/LCAOCalculator/LCAOCalculator.html#lcaocalculator-c), which allows one to set the total spin moment of the system. For example, for the AFM solution, you should do a spin-polarized calculation with the spin moments set as described above, and set fixed_spin_moment = 0.

Best regards,
Daniele

18

General Questions and Answers / Re: different transmission for unit cell and device

« on: May 8, 2019, 10:40 »

Hello,

what do you mean by different values? The first thing to be check is the consistency between the transmission spectra calculated with the two methods. This is because the calculation of the transmission spectrum is done using two different methods depending on whether one uses a BulkConfiguration or a DeviceConfiguration.

Could you paste the transmission spectra calculated for the BulkConfiguration  and DeviceConfiguration, together with the scripts used for those calculations?

Best,
Daniele

19

General Questions and Answers / Re: Optical Spectrum - Optical Conductivity

« on: April 1, 2019, 10:23 »

Hi Nicola,

try to change following statement in the script '(16,0) CNT STD.py':

# Repeat the configuration 3 times in each direction
bulk_configuration = configuration.repeat(1, 1, 3)

to


# Repeat the configuration 3 times in each direction
bulk_configuration = configuration.repeat(1, 1, 1)

the bulk configuration used in the SpecialThermalDisplacement class should be consistent with the that used in the script '(16,0) Carbon Nanotube DynMat.py', not with the number of repetitions used in the dynamical matrix class. 

Best,
Daniele

20

General Questions and Answers / Re: how to use ParallelDevicePerformanceProfile

« on: March 22, 2019, 11:48 »

Hi,

yes, it has to be done by scripting. The easier workflow is:

1) Create the script you need using the Script generator.

2) Send it to the editor

3) Comment out the line:
device_configuration.update()

4) Add the following line, including the desired values for processes and threads:
profile = ParallelDevicePerformanceProfile(device_configuration, processes_and_threads=[(1, 1), (1, 2), (2, 1)])
 
Best,
Daniele

21

General Questions and Answers / Re: Correction of formation energy of charged defect for monolayer 2D materials

« on: March 18, 2019, 10:13 »

Dear PA-Chen,

you are right, the formation energy of charge defects can only be calculated for 3D objects within QuantumATK. Using similar methods for 2D materials is still subject of active research, see for example:
https://iopscience.iop.org/article/10.1088/2053-1583/aa6811/meta

Best regards,
Daniele

22

General Questions and Answers / Re: Is Dynamical matrix and Hamiltonian Derivative Independent of Spatial region

« on: March 7, 2019, 13:31 »

Hi,

that depends on whether you want to include the effect of the gate or not:

1) if you don't want to include the effect of the gate on the inelastic current, using the phonons and dHdR calcuated at V_GS = 0 V is sufficient.

2) if you want to include the effect of the gate in the calculated inelastic transmission spectrum, then you will have to recalculate the phonons and dHdR for each value of V_GS.

Both approaches are valid, as long as you know which effects are taken into account and which are not in your calculation.

Best,
Daniele

23

General Questions and Answers / Re: Is there a way to calculate the local inelastic current?

« on: March 7, 2019, 13:23 »

Hi Weixiang,

no, that is not really possible, because the inelastic current is calculated based on the electron-phonon coupling matrix, which has both local and non-local terms.

Best,
Daniele

24

General Questions and Answers / Re: Is it possible to calculate Inelastic current for defective device configuration

« on: February 22, 2019, 10:02 »

Dear Weixiang,

yes, it is possible to use the InelasticTramissionSpectrum class to calculate defective structures. In this case you will have to explicitly calculate the dynamical matrix and Hamiltonian derivatives of the entire region around the defect, that is, it will not be possible to use the phonon band structure and Hamiltonian derivatives of the bulk electrodes.

See:
https://docs.quantumatk.com/tutorials/inelastic_current_in_si_pn_junction/inelastic_current_in_si_pn_junction.html

Best regards,
Daniele

25

General Questions and Answers / Re: the inelastic current is needed to taken into account if the channel is short

« on: February 20, 2019, 12:54 »

if we consider the temperature effect on the transport properties? it is necessary to take the inelastic current into account although the short channel about 1nm?

That depends a lot on the type of device and geometry. In the case of e.g. molecular or graphene-like junctions, the effects of electron-phonon coupling can be quite large, even if the actual "channel" is rather short. See e.g. PHYSICAL REVIEW B 93, 245415 (2016).

The best thing is to try to do the actual calculation.

Best,
Daniele

26

General Questions and Answers / Re: it is the channel too short to make PLDOS of p-i-n junction looks like that

« on: February 20, 2019, 09:25 »

The PLDOS shows clearly that the channel is too short. The PLDOS should be flat in the vicinity of the left and right boundaries. See, e.g., Fig. 1 in PHYS. REV. APPLIED 10, 014026 (2018).

Best regards,
Daniele

27

General Questions and Answers / Re: the inelastic current is needed to taken into account if the channel is short

« on: February 19, 2019, 09:14 »

That really depends on the electronic structure of the device throughout the channel. It is difficult to say anything without having done the actual calculation.

If you find that the current through the device is particularly small, then inelastic effects might be important.

Best,
Daniele

28

General Questions and Answers / Re: the inelastic current is needed to taken into account if the channel is short

« on: February 18, 2019, 09:21 »

Hi,

Yes, temperature effects might still be important and affect the transport through the device, see, e.g., the cases treated in:

First-principles electron transport with phonon coupling: Large scale at low cost
Tue Gunst, Troels Markussen, Mattias L. N. Palsgaard, Kurt Stokbro, and Mads Brandbyge Phys. Rev. B 96, 161404(R)
https://journals.aps.org/prb/abstract/10.1103/PhysRevB.96.161404

Best regards,
Daniele

29

General Questions and Answers / Re: Bravais lattice type for DOS calculation

« on: February 18, 2019, 09:16 »

Hello,

the Gamma point is always positioned at the center of the Brillouin zone, independently on the specified lattice type. In the DOS calculator, the k-point grid will be shifted so that one of the grid points is positioned at Gamma = [0.0,0.0,0.0].

Best,
Daniele

30

General Questions and Answers / Re: NEB image

« on: February 12, 2019, 09:19 »

Dear Dipankar,

it is indeed possible. In order to do it, you should import the full NEB configuration in the Builder. In the Builder, it is then possible to extract each of the NEB images.

Best  regards,
Daniele